Sued for an unpaid invoice in the UK, your defence options

You open your post one Tuesday and find a claim form (N1). Someone is suing you in the county court for an unpaid invoice. £4,500. Thirty years in business, and you've never been to court. Your stomach drops.

The good news: you almost certainly have a defence. You may not have paid because goods never arrived, because what arrived was broken, because you already paid, or because the invoice itself was wrong. Or you might owe some of it, but not all of it. This guide walks you through every option available to you, the forms you need to file, and the deadlines that matter.

The short version

You have 14 days from delivery of the claim form to acknowledge service on form N9 (you can do this online at HMCTS online or post it). You then have up to 28 days total to file your defence on form N9B. The most common defences are: no contract was agreed, goods were never delivered or were defective, you already paid, you have a counterclaim, or the claim is too old (statute-barred after 6 years). Filing a defence stops judgment by default. If you file nothing, you lose by default and the claimant gets a judgment against you.

At a glance

Step 1: Check the claim and the invoice carefully

Before you panic, read the claim form (N1) word by word.

What to look for:

• Invoice number and date. Does the claimant have the right invoice? Is the date correct?
• Amount claimed. Is it the exact amount you owe? Many invoices include payment terms (Net 30, Net 60) or conditions. If you paid a partial sum, the claim should reflect that.
• Goods or services described. Do you recognise the work described? Is it accurate?
• Payment terms. Did the invoice state "Net 30" or "immediate payment"? When was payment due?
• The claimant's signature block. Is it the right company/person suing you?
• Service of the claim. How was it delivered to you? Was it to the right address?

Many claims collapse because the claimant has the wrong invoice, the wrong amount, or served the wrong defendant. If you spot an error, keep it. You'll use it later.

Also check: have you already paid this invoice? Look at your bank statements for the last 6 months. If you paid but the claimant is claiming you didn't, that's a complete defence.

Step 2: Acknowledge service (N9) within 14 days

You do not have to file a full defence immediately. You have 14 days from delivery of the claim form to file an Acknowledgment of Service (form N9). This tells the court: "Yes, I got the claim, and I'm preparing my defence." Filing N9 automatically extends your deadline to file a full defence from 14 days to 28 days.

Why file N9?

• It stops the claimant obtaining judgment by default (i.e., winning without a hearing because you didn't respond).
• It gives you 14 extra days to gather evidence, collect bank statements, emails, and contract terms.
• It signals to the claimant that you're taking the claim seriously, which sometimes prompts settlement discussions.

How to file N9:

Go to the HMCTS online court portal (www.gov.uk/respond-county-court-claim), log in with your email, and file the form. You can also post a hard copy to the court address on the claim form. Filing is free.

Step 3: Consider your defence position

Now you have 14 days (from day 14 to day 28) to work out your answer. Write down everything you can remember about this transaction: emails, purchase orders, delivery notes, communications with the claimant, partial payments made, complaints about the goods/services.

Ask yourself:

1. Did you ever agree to this deal?
2. Did you receive the goods or services?
3. If yes, were they what was promised, or were they faulty?
4. Did you actually pay?
5. Do you have a counter-claim (e.g., they owe you money too)?
6. Is the claim really old (more than 6 years)?

The answer to these questions will shape your defence.

Defence route: No contract or agreement

The claim:

You never agreed to buy the goods or services. Perhaps a salesman sent an unsolicited invoice, or the claimant confused you with another customer.

The evidence you need:

• Emails showing you rejected the offer.
• Proof you never ordered anything (e.g., your purchase order was for a different item).
• Communications where you said "no thanks."

Why this works:

A contract requires offer and acceptance. If you never accepted the offer, there is no contract. The claimant has to prove you agreed. If the evidence is ambiguous, the court will decide based on what a reasonable person would conclude from the facts.

Example:

A supplier sends you an unsolicited quotation. You don't reply. Three months later, they invoice you and sue. They have no proof you ordered anything. This is a complete defence.

Defence route: Goods or services not delivered or defective

The claim:

You agreed to the deal, but the goods never arrived, or they arrived damaged, or the service was never performed. Or the goods/service were so defective that they were not what was contracted for.

The evidence you need:

• Delivery notes showing goods were not received.
• Emails saying "goods still haven't arrived" or complaints about damage.
• Photos of damaged goods.
• Emails or messages to the claimant saying "this is broken" or "this doesn't work."
• Your complaint to them (in writing) before the claim was filed.
• If a service: proof the work was never done (e.g., website was never built, cleaning was never done).

Why this works:

If the claimant didn't deliver the goods or services they promised, you have no obligation to pay. This is the core principle of contract law: both sides must perform. The claimant can't sue you for payment if they failed to deliver.

Important nuance:

If the goods arrived late but eventually arrived, or if the service was poor but completed, this is not a defence to the full amount. Instead, you might claim a reduction in price (damages for breach). This becomes a counterclaim or a mitigation argument at trial.

Example:

You ordered a website design for £4,500. The designer went silent after you paid a 50% deposit. The website was never delivered. You have a complete defence to the full invoice. You might also claim to get your £2,250 deposit back (counterclaim).

Defence route: Statute-barred (6 years for simple contract)

The claim:

More than 6 years have passed since the invoice date, and no acknowledgment or part-payment has been made in the last 6 years.

The statute:

Limitation Act 1980, section 5. Simple contract claims (written or oral) must be brought within 6 years of the breach. If more than 6 years have passed, the court has no power to grant judgment, even if the claim is true.

The evidence you need:

• The invoice itself, showing the date.
• Proof of the last communication or payment. If you made a payment towards the invoice (even £1) within the last 6 years, the clock resets.
• Any written acknowledgment of the debt you made within the last 6 years.

Why this works:

The law recognises that old debts should not hang over you forever. After 6 years of silence, the law presumes the debt is stale. This is a hard defence: if the 6-year period has passed, the court cannot order you to pay, full stop.

Critical trap:

If you've made a payment towards this invoice in the last 6 years, even a small one, the clock resets. The claim is no longer statute-barred. Make sure you check your bank statements carefully.

Example:

An invoice is dated 1 January 2018. The claimant sues you on 15 May 2024. That's over 6 years. You never paid anything after 1 January 2018. This is a complete defence. The claimant's claim is too old.

Defence route: Payment already made

The claim:

You paid the invoice, but the claimant claims you didn't. This is the simplest and cleanest defence.

The evidence you need:

• Bank statement showing the payment left your account.
• The date the payment was made.
• Proof of who it was paid to (e.g., the claimant's bank details).
• Any receipt or acknowledgment from the claimant that payment was received.
• If you paid by cheque: a cancelled cheque or bank record.
• If you paid by direct transfer: the transaction reference.

Why this works:

Payment discharges a debt completely. If you've paid, you owe nothing more. The burden is on the claimant to prove you haven't paid. If you have bank evidence that the money left your account and went to them, that is almost conclusive proof.

Common wrinkle:

The claimant might say "We never received it" or "You sent it to the wrong bank account." If your bank confirms the payment reached their account (or an account in their name), you have a rock-solid defence. If there's genuine doubt about whether the payment reached them, this becomes a disputed question of fact that a judge will decide.

Example:

You sent £4,500 via bank transfer to the claimant's account on 10 February 2023. Your bank statement proves it. The claimant sues on 15 May 2024 claiming non-payment. You have a complete defence: you paid it.

Defence route: Set-off and counterclaim

The claim:

You agree you owe some of the money, but the claimant owes you money too (perhaps for defective work, or for goods you supplied them that they didn't pay for). You want to offset what they owe you against what you owe them.

The two concepts:

• Set-off: You admit the debt but argue you have an equal or larger counter-debt that wipes it out.
• Counterclaim: You claim damages or money back from the claimant in the same case.

These are different but often go hand-in-hand. For example: "You're right, I haven't paid your invoice for £4,500, but you owe me £6,000 for the defective work you did. I'm setting off your £4,500 against my claim for £6,000, leaving you owing me £1,500."

The evidence you need:

• Proof of your counter-debt: invoices you sent them, estimates, quotes, emails describing the problem, photos of damage.
• An explanation of why they owe you the money.
• Ideally, a demand letter you sent to them before they sued you (shows you were asserting the counter-debt).

Why this works:

Equity and fairness. If both parties owe each other money on related matters, the debts can be set against each other. You don't have to pay them in full if they owe you part of it back.

Important limits:

The counter-debt must be related to the same transaction or closely connected. You can't set off an unrelated debt. For example, if they're suing you for an unpaid invoice for web design, you can set off their failure to deliver a logo, but you probably can't set off an old debt from 2010 for something totally different.

Example:

They invoice you for £4,500 for website work. The website has never been updated and doesn't work properly. You spent £2,000 fixing it yourself. You file a defence admitting you owe £4,500 but counterclaim £2,000 for the defective work. The net claim is £2,500.

Defence route: Improper service / wrong defendant

The claim:

The claim form was not properly served on you, or you're the wrong defendant altogether.

Improper service:

The claim form must be delivered to you personally, or to an authorised agent, or to your place of business. If it was left with someone unauthorised, or served on the wrong address, that's improper service. You can file a defence and argue the court has no jurisdiction over you.

Wrong defendant:

Perhaps you're a sole trader and they've sued your company by mistake. Or they've sued "John Smith Ltd" when your company is "John Smith Holdings Ltd." If they've sued the wrong legal entity, you have a strong defence.

The evidence you need:

• Proof of how the claim was served (the service documents will say).
• Proof you never received it at the address stated (if that's your argument).
• Evidence of your correct legal name or entity.
• Proof you operate from a different address.

Why this works:

The court can only make orders against people it has properly served. If service was improper or the defendant is wrong, the court may set aside (cancel) the judgment and the claimant will have to start again.

Tactical note:

This defence is less likely to succeed than "I didn't owe the money" because courts are forgiving of minor service defects. But if you can show you genuinely never received the claim form, or that you are a completely different legal entity, you have a good argument.

Late Payment of Commercial Debts (Interest) Act 1998 (the claimant's powerful weapon)

You need to understand this Act because the claimant will almost certainly cite it. It gives them a significant advantage, and you need to know what you're up against.

What the Act does:

If you're a small business or freelancer, and you owe a commercial debt (payment for goods or services), and the invoice states payment terms (e.g., "Net 30"), and you miss the deadline, the claimant can automatically claim statutory interest on top of the unpaid amount.

The interest rate:

Bank of England base rate + 8%. Currently (2026), that's roughly 13% per year, compounding daily.

Example:

An invoice for £4,500 issued 1 January 2025 with "Net 30" terms is due 31 January 2025. You don't pay. By 1 May 2026 (16 months later), the claim is for £4,500 + statutory interest of roughly £800 = £5,300 total.

Why you need to know:

Even if you have a valid partial defence (e.g., the goods were defective and worth 20% less), the claimant can still claim interest on the undisputed part. If you're negotiating a settlement, the statutory interest is a huge cost that accrues every day you don't pay. This often forces small businesses to settle rather than fight, even when they have a defence.

Your counter-move:

Check the invoice. If it does NOT state payment terms, the claimant cannot automatically claim statutory interest under the Act. They'd have to prove loss (e.g., the cost of borrowing money to cover the unpaid amount), which is harder to do.

Also, if you have a valid defence to part of the invoice, argue that the statutory interest should be reduced proportionately.

Step 4: File defence (N9B) within 28 days

Once you've gathered your evidence and decided on your defence, you must file form N9B (Defence) within 28 days of the claim form being served on you.

What to include in your N9B:

• A clear, numbered statement of the facts you rely on (e.g., "The claimant claims £4,500 for website design. I admit I instructed them to build a website, but the website was never delivered. I have not paid because the service was never performed.").
• Your defence to each part of the claim.
• Any counterclaim (on a separate section of the form).
• A statement of truth (a declaration that you believe the facts are true, signed under penalty of perjury).

How to file:

Online via the HMCTS court portal (easiest), or by post to the court address. Filing is free.

What happens next:

The court will allocate the claim to a track: small claim (under £10,000), fast track (£10,000 to £100,000), or multi-track (over £100,000). For an unpaid invoice of £4,500, this will be a small claim.

Step 5: Allocation, mediation, hearing

Small claim track (claims under £10,000):

Once you've filed your defence, the court will send both you and the claimant an Allocation Questionnaire (form N149). You fill it in and tell the court: Do you want a hearing? Can you settle? What's the value of the dispute? How much will a hearing cost?

Many cases settle at this stage because both parties realise a hearing will cost more than the dispute is worth.

Mediation:

The court may suggest mediation (a neutral person helps you both negotiate). This is often faster and cheaper than a hearing. If you want to try mediation, both parties can agree to pause the case and talk.

Hearing:

If neither side settles, the case goes to a hearing. This is usually a telephone or video call with a judge. You'll present your evidence (your witness statement, documents, bank statements, emails). The claimant will present theirs. The judge will decide on the balance of probabilities: is it more likely than not that the claimant has proved their case?

For a small claim, the loser normally pays their own legal costs, not the winner's. This limits the financial risk.

Day to day (timeline)

Common misconceptions

"I can ignore the claim form because I'm small."

False. The court doesn't care how big you are. If you ignore the claim, judgment will be entered against you by default. Your wages can be garnished, your bank account frozen, your goods seized.

"I can just phone the claimant and work it out."

You can try, and many disputes settle this way. But once a claim is filed, the court is involved. Ringing them up is fine, but you still need to file your defence by day 28 in case negotiations fail.

"Statutory interest is not real."

It absolutely is. The claimant can claim it by right under the Late Payment of Commercial Debts (Interest) Act 1998. It accrues daily and compounds. By the time you go to court, you might owe 30% more than the original invoice.

"If the claimant got the amount wrong, I don't have to pay anything."

Wrong. If they've overcharged by £100 on a £4,500 invoice, you still owe them £4,400. You'd file a defence disputing the overcharge, and the court would decide the right amount.

"I can defend the case without evidence."

You need evidence. Your word alone (a "bare denial") is not enough. You need bank statements, emails, purchase orders, delivery notes, or witnesses. The claimant has to prove their case, but if you say "I paid" and offer no evidence, you'll lose.

"The court will side with the little guy."

The court applies the law fairly to both parties. If you owe the money and have no defence, you'll lose, regardless of size. If you have a valid defence, you'll likely win, regardless of size.

Related concepts

• Responding to a court claim: the N9 form
• Filing your defence: the N9B form
• Small claims track explained
• Counterclaims and set-off
• Evidence gathering for court
• Limitation periods and the Limitation Act 1980
• Late payment interest under the 1998 Act
• Settlement and mediation before trial
• Witness statements in small claims

Sources

• UK Government, "Respond to a court claim" (2024): www.gov.uk/respond-county-court-claim
• Legislation.gov.uk, "Late Payment of Commercial Debts (Interest) Act 1998": www.legislation.gov.uk/ukpga/1998/20
• Legislation.gov.uk, "Limitation Act 1980": www.legislation.gov.uk/ukpga/1980/58
• Citizens Advice, "Court claims and orders" (2024): www.citizensadvice.org.uk
• HM Courts & Tribunals Service, "Small claims guide" (2024): www.gov.uk/courts-tribunals/county-courts

Disclaimer: This page provides information about defending unpaid invoice claims in the UK. It is not legal advice. Court procedure changes regularly. Before filing your defence, confirm the current deadlines and forms with the court or consult a solicitor. If you need professional legal representation, contact a solicitor specialising in small claims or commercial disputes.

Written by Peter Kolomiets, founder of CaseCalm. UK content reviewed 2026-05-28.