How to use ChatGPT to write invoices and chase late payments (UK trades)

Getting the words of an invoice right is not the same as getting paid. A chat tool can turn your job notes into a clear bill, and it can draft the message you send when that bill sits unpaid. It cannot see your bank, and it should not invent a legal threat. You still decide what is owed, who owes it, and when you ask.

Shaun, 20+ years in UK construction, chases his own invoices the same way this guide suggests: facts first, tone second, and the late-payment rules only where they actually apply. We search the AI world every week so you don't have to.

What a UK invoice needs

GOV.UK says an invoice must include (opens in a new tab):

• a unique identification number
• your company name, address, and contact information
• the company name and address of the customer
• a clear description of what you are charging for
• the date the goods or service were provided
• the date of the invoice
• the amount being charged
• the VAT amount if it applies
• the total amount owed

If you are a sole trader, GOV.UK also says the invoice must include your name and any business name you are using, and an address where legal documents can be delivered if you use a business name.

VAT invoices carry more detail, and GOV.UK says you must use a VAT invoice if you and your customer are both VAT registered. If you are not VAT registered, do not let a draft add a VAT number or a VAT line. Put that in the prompt so it cannot drift.

Payment details are what get you paid: the account name, sort code, and account number, or the payment link you actually use. Write them in the prompt. Do not ask the tool to make them up.

A prompt that drafts the invoice from your notes

Paste the notes. Leave blanks where you are unsure. The square brackets are for you to fill, not for the tool to guess.

Draft a UK invoice from these notes. UK English. Do not invent prices, dates, quantities, addresses, or bank details. If something required is missing, write [missing: what] and leave it blank.

- Invoice number: [number]
- Invoice date: [date]
- Supply date: [date the work was done]
- My name and trading name: [name]
- My address and phone or email: [contact]
- Customer name and address: [customer]
- Description of the work: [what you did, room by room if needed]
- Amount: £[amount]
- VAT: [not VAT registered, so no VAT / VAT at 20%, VAT amount £[amount]]
- Total owed: £[total]
- Bank details: [account name, sort code, account number]
- Payment due: [date, or "within 14 days"]

Lay it out so I can paste it into an email or a document. Put the total near the top. Do not add a late-payment warning unless I have written one in the notes.

Read every figure against the quote they accepted. If the quote excluded decoration, the invoice should not suddenly include it. If you did extra work, say what the extra was and the price you agreed at the time. A surprise line is how a fair bill becomes an argument.

Send the invoice to the address you were given, and keep a copy of what you sent and when.

When you chase, start with the facts

A lot of late payments are not a refusal. The invoice went to the wrong person, or it was missing a purchase order number, or someone was on holiday. The first message should make it easy to pay, and easy to tell you what is stuck.

Wait until the date you wrote on the invoice has passed. Then send a short note. This prompt keeps your tone polite and does not add interest or threats.

Write a short, polite payment reminder I can send by email or WhatsApp. UK English. Under 120 words.

Facts. Do not change them:
- Customer: [name]
- Invoice number: [number]
- Amount: £[amount]
- Invoice date: [date]
- Due date: [date]
- How they can pay: [bank details or "the details are on the invoice"]
- Work it was for: [one line]

Ask them to pay, or to tell me if something on the invoice is wrong. Do not mention interest, courts, or debt collectors. Do not apologise for asking.

If they reply that the invoice never arrived, send it again and keep the same number. If they say a line is wrong, sort that in writing before you chase the rest.

A firmer chaser, still without inventing the law

If the polite note gets nothing, the next one can be firmer. Firm means clear about what you will do next. It does not mean insults, and it does not mean a legal claim you have not checked.

Decide your next step before you write. That might be "I will pause any further work on your other job" or "I will pass this to a solicitor" only if you are actually willing to do that. Do not let the draft choose a threat for you.

Write a firmer payment chase for a UK tradesperson. UK English. Calm and specific. No insults.

Facts. Do not change them:
- Customer: [name]
- Invoice number: [number]
- Amount still unpaid: £[amount]
- Original due date: [date]
- Date of my last reminder: [date]
- What I will do if it is still unpaid 7 days after this message: [write the real next step, or leave as "I will write again"]

Say what is owed, that it is overdue, and the date I now need it paid by (7 days from today). Do not add statutory interest, compensation, court, or a debt collector unless that next step is written above. Do not invent a contract clause.

Send it to the same person you invoiced, and if a business has an accounts email, send it there as well. Keep both messages.

Business customers and the late-payment rules

This part is only for commercial debts. That means another business owes you for goods or a service. It is not a way to add interest to a homeowner's kitchen.

The law is the Late Payment of Commercial Debts (Interest) Act 1998. GOV.UK explains when a commercial payment becomes late (opens in a new tab), and how statutory interest works (opens in a new tab).

From those GOV.UK pages, in plain words:

• If you agreed a payment date, it must usually be within 30 days for public authorities, or 60 days for business transactions. You can agree longer than 60 days for a business customer only if that longer period is fair to both businesses.
• If you did not agree a payment date, the payment is late 30 days after the customer gets the invoice, or 30 days after you deliver the goods or provide the service if that is later.
• Statutory interest on a business-to-business debt is 8% plus the Bank of England base rate. You cannot claim statutory interest if the contract already sets a different interest rate. You cannot use a lower interest rate in a contract with a public authority.
• The base rate changes. GOV.UK tells you to check the current Bank of England base rate, and it gives a worked example rather than a rate you should assume today. In that example, a debt of £1,000 at a base rate of 0.5% would be £85 of statutory interest across a year, about 23p a day. Use the current base rate when you do your own sum. Do not copy the 0.5% figure unless that is actually the rate that applies.
• You can also claim a fixed sum for debt recovery costs (opens in a new tab), once per late payment. GOV.UK sets the amounts at £40 up to £999.99, £70 from £1,000 to £9,999.99, and £100 for £10,000 or more. Those amounts come from the late-payment legislation. GOV.UK also says a supplier can claim reasonable recovery costs on top, where the fixed sum does not cover them.

Interest and the fixed sum are claims you choose to make. They are not added by magic, and a chat tool does not know your contract. If the customer is a homeowner, leave this section out of the message entirely.

A prompt for a business-to-business chaser

Use this only when the customer is a business and you have read the GOV.UK pages for the job in front of you. The prompt is written so the draft cannot bolt on a court threat or a percentage you did not supply.

Write a payment chase to a UK business customer. UK English. Factual.

The customer is a business, not a householder. Do not say I will take them to court. Do not state an interest percentage unless I have typed one below.

- Customer: [business name and contact]
- Invoice number: [number]
- Principal still unpaid: £[amount]
- Due date: [date]
- Days overdue: [number]
- Statutory interest I have calculated, if I want it mentioned: [£ amount, or "do not mention interest"]
- Fixed recovery sum I want mentioned, if any: [£40 / £70 / £100 / do not mention]
- Pay by: [date]
- Payment details: [as on the invoice]

Explain that the invoice is overdue. If I have entered an interest amount or a fixed sum, mention those figures once and say they are claimed under the Late Payment of Commercial Debts (Interest) Act 1998. If I wrote "do not mention", leave them out. Ask them to pay the principal by the date above. Invite them to tell me if they dispute the invoice.

Before you send it, check three things. The customer really is a business. The due date matches the invoice. Any interest figure is one you worked out from the current base rate, not a number the draft invented. GOV.UK's interest page (opens in a new tab) is the page to keep open while you do that sum.

If they dispute the work, pause the interest conversation and deal with the dispute. Adding a sharper letter on top of a genuine snag does not get the wall repaired.

The UK Trades AI Prompt Pack has copy-paste prompts for quotes, chasing payment, tax admin, and customers. It is free when you sign up to the weekly email, on the home page.