How to Invoice Clients Professionally in the UK — Legal Requirements and Best Practice

What must a UK sole trader invoice include?

HMRC does not specify a particular invoice format for non-VAT-registered businesses, but a professional invoice should include:

• Your business name (the name you trade under)
• Your contact details (address, email, phone)
• The client's name and address
• A unique invoice number (for your records)
• The invoice date
• A description of the goods or services provided
• The quantity and unit price (if applicable)
• The total amount due
• Your payment terms (e.g., "Payment due within 30 days of invoice date")
• Your bank details or payment method

For simplicity, use consistent numbering (INV-001, INV-002, etc.) from your first invoice. This makes tracking easier and looks professional.

What a VAT-registered business must include additionally

If you are VAT-registered, your invoices must also include:

• Your VAT registration number (format: GB followed by 9 digits)
• The rate of VAT applied to each item (or that the supply is zero-rated or exempt)
• The amount of VAT charged
• The net amount before VAT
• The gross amount including VAT

A simplified VAT invoice (for sales under £250) can include a shorter set of details, but a full VAT invoice is required for larger amounts and is always safer.

Payment terms — what is standard in the UK?

The standard payment term for UK B2B invoices is 30 days from the invoice date. Under the Late Payment of Commercial Debts (Interest) Act 1998, if payment is not made within agreed terms (or 30 days if no terms are stated), you are legally entitled to charge:

• Statutory interest at 8% above the Bank of England base rate
• A fixed debt recovery cost of £40-£100 depending on invoice size

In practice, most small businesses do not exercise these rights to preserve client relationships. But knowing you have them gives you a firmer basis for chasing overdue invoices.

Practical steps to get paid faster

Invoice immediately. Do not wait until the end of the month to send invoices for work completed. Invoice on completion or at agreed milestones.

Be clear about what you are charging for. Vague invoice descriptions lead to queries that delay payment. "Bookkeeping services — March 2026" is clearer than "services rendered."

Make payment easy. Include your bank sort code and account number on the invoice. If you use PayPal or Stripe for smaller payments, include the link.

Use accounting software. Xero and QuickBooks allow you to send invoices by email directly from the software, track which invoices are viewed and unpaid, and send automatic payment reminders at configurable intervals (7 days, 14 days, overdue).

Phone rather than email for seriously overdue invoices. A polite phone call is more effective than a third email reminder. Keep the tone professional — late payment is often administrative, not deliberate.

Handling a disputed invoice

If a client disputes an invoice, respond in writing within 24-48 hours. Acknowledge the dispute, outline the agreed scope, and provide any supporting records (timesheets, project scope documents, email correspondence). Resolve minor disputes swiftly — the cost of a small credit note is less than the cost of a relationship ending badly.

For invoices that remain unpaid after 60-90 days with no dispute raised, consider using a formal letter before action template. Most unpaid invoices are resolved at this stage without going to the Small Claims Court.

Recording invoices in Xero or QuickBooks

Once sent, mark invoices in your accounting software immediately. This ensures your debtors list is always current, your management accounts reflect actual outstanding income, and your bank reconciliation matches invoices to payments correctly. Never bypass the invoicing module by just recording income directly from the bank — you lose the audit trail and the debtor visibility.