An invoice is a formal, legally binding document issued by a seller to a buyer to request payment for goods or services. It serves as a key attachment in the company’s accounting records and is essential for proper recording of sales revenue and VAT. A bill is a more general term for a payment request and is discussed in more detail in the article Bill.

For a comprehensive overview of VAT (Value Added Tax), see What is VAT (VAT)? .

Invoices document sales that contribute to the company’s turnover and are the natural outcome of a contractual agreement when a sale has been agreed and delivery has taken place. Invoices also play a vital role in procurement processes, where correct invoice handling is crucial for effective supplier management.

For a detailed introduction to issuing and managing invoices, see Invoicing.
For guidance on verifying and authorising incoming invoices, read Invoice Approval.

Many companies utilise modern invoice software to automate and streamline sending, follow-up, and integration with accounting systems.

Section 1: The Structure of an Invoice

In the UK, the content of an invoice is governed by accounting regulations. To be valid, an invoice must include certain mandatory information. Many companies use standardised invoice templates to ensure compliance with legal requirements and to maintain a professional brand image.

Statutory Content Requirements:

  1. Invoice number: A unique, sequential number assigned automatically.
  2. Invoice date: The date the invoice is issued.
  3. Seller’s Name and Company Registration Number: Clear identification of the seller. If VAT-registered, the VAT registration number must be included.
  4. Buyer’s Name and Address: Clear identification of the customer.
  5. Description of Goods/Services: A clear, unambiguous description of what has been supplied.
  6. Date and Place of Delivery: When and where the goods/services were delivered.
  7. Price and VAT: The total amount in GBP, with VAT shown separately at the applicable rate according to the VAT Act.
  8. Total Amount: The total payable sum.
  9. Payment Due Date: The deadline for payment.

Section 2: Types of Invoices

While the standard sales invoice is most common, there are various types of invoices used in different contexts. In modern retail, invoices and receipts are often generated automatically via point-of-sale (POS) systems, ensuring accurate documentation and seamless integration with accounting software.

2.1 Sales Invoice

This is the most typical invoice, serving as a direct request for payment for goods or services delivered. It records income in the seller’s accounts and an expense in the buyer’s accounts. When companies sell on credit, a credit sale arises, requiring systematic follow-up and credit risk management.

In B2B transactions, sales invoices tend to be more detailed, with longer payment terms (usually 30-90 days), reference numbers, and specific documentation such as contract or delivery references.

For companies seeking to eliminate credit risk altogether, cash sales can be an option, where payment is required immediately upon delivery.

2.2 Credit Note

A credit note is a “negative invoice”. It is issued to correct, reduce, or cancel a previously issued invoice. This might be necessary in cases of returned goods, price reductions, or errors in the original invoice. A credit note must always reference the original invoice number.

For more details on when and how to issue credit notes, including legal and accounting considerations, see our comprehensive guide to credit notes.

2.3 Pro Forma Invoice

Pro forma invoices are preliminary invoices used mainly as quotations or estimates. They are sent to customers to provide an approximate cost before the final delivery. A pro forma invoice does not create a payment obligation and should not be recorded as income or expense.

Main features of a pro forma invoice:

  • Preliminary offer: Outlines expected prices and delivery terms.
  • No accounting entry: Cannot be recorded in the company’s books or VAT returns.
  • Clear labelling: Must be marked as “Pro forma invoice” to distinguish from a real invoice.
  • Export use: Often used for customs and export documentation.

2.4 eInvoice (Electronic Invoice)

E-invoicing is the standard for electronic invoicing in the UK, transmitted digitally and processed automatically via the PEPPOL network and integrated accounting systems. For more, see our guide to electronic invoicing.

Section 3: Invoice Processing and Certification

Once an invoice is received through the document receipt process, it must undergo a control and approval process before posting and payment. This process, known as authorisation, is a vital part of internal controls.

For a detailed overview of the entire process for incoming invoices, including control routines, automation, and best practices, see our comprehensive guide.

Checks for Invoices

Before approval, the following checks should be performed:

  • Factual verification: Has the product or service been delivered as described?
  • Accounting control: Is the invoice correctly posted, with VAT properly accounted for?
  • Financial control: Is the purchase within budget and authorised limits?

Proper invoice authorisation ensures the company only pays for goods and services actually received, with all transactions properly documented. For guidance on modern document handling, including digital solutions and best practices, see our detailed guide. This is crucial for maintaining internal control and satisfying audit requirements.

Automating Invoice Processing

Many modern businesses use invoice recognition technology. This employs OCR (Optical Character Recognition) and AI to automatically read, interpret, and process invoices, reducing processing time by up to 80-90% and minimising human error.

Section 4: Payment Methods for Invoices

After approval, invoices must be paid by the due date. Several payment methods are available for individuals and businesses:

Automated Payment Solutions

For regular invoices, automatic payment options can save time and reduce errors:

  • Direct Debit: The most common method for recurring payments. The amount is automatically debited from the bank account on the due date.
  • E-invoice: Electronic invoice received directly in accounting or banking platforms, requiring approval for each payment.

Digital invoicing and payment solutions are increasingly prevalent. For more, see our guide to electronic invoicing.

All these digital payment options are part of the broader payment services landscape, regulated by the Payment Services Regulations 2017 (equivalent to PSD2), ensuring security and innovation.

Manual Payment Methods

  • Bank Transfer: Traditional method via online banking or bank branch, often with reference numbers for reconciliation.
  • Payment reference: A unique reference number that automatically links the payment to the correct invoice or customer account.
  • Mobile Payment Apps: Such as Paym or Banking apps like Monzo, Starling, or Revolut.

The choice depends on invoice type, amount, and control preferences. For regular payments like rent or subscriptions, Direct Debit is often the most practical.

Section 5: Invoice Fees and Additional Costs

In addition to the principal amount, suppliers may charge invoice fees to cover administrative costs. This is common when customers opt for paper invoices instead of electronic ones.

Common Additional Charges

  • Paper invoice fee: Covers postage, printing, and manual processing.
  • Dispatch fee: For special delivery or additional documentation.
  • Late payment interest: Charged if payment is overdue, regulated by the Late Payment of Commercial Debts (Interest) Act 1998.

Important: All additional fees must be reasonable, agreed in advance, and reflect actual costs. Electronic alternatives should be provided free of charge where applicable.

For detailed legal and accounting guidance on invoice fees, see our comprehensive guide to invoice charges.

Section 6: Follow-up on Unpaid Invoices

When invoices are unpaid past the due date, systematic follow-up is essential to recover the debt. This process is part of credit control and directly impacts the company’s liquidity. Maintaining an accurate customer database is fundamental for effective follow-up.

Payment Reminders

The initial step is sending payment reminders. These are formal requests for payment, which must comply with legal requirements:

  • First reminder: Usually sent 30 days after the due date, politely.
  • Second reminder: More assertive, possibly with a late fee.
  • Final reminder: Warning of legal action or debt collection.

Consequences of Non-Payment

Unpaid invoices can lead to:

  • Late payment interest: Statutory interest from the due date.
  • Debt collection fees: Administrative costs for follow-up.
  • Debt collection proceedings: Transfer to a debt collection agency.
  • Credit record entries: Such as a County Court Judgment (CCJ), which can affect creditworthiness for years.
  • Impairment/write-off: Recognising uncollectible debts.

Effective follow-up reduces bad debts and improves cash flow. For a detailed process, see our guide on debt recovery .

Section 7: Summary

Invoices are fundamental to UK accounting, documenting sales, VAT, and payment. To ensure compliance and accuracy, you should:

  • Use complete and compliant invoice content in line with legal requirements.
  • Select the appropriate invoice type (sales invoice, credit note, pro forma, e-invoice).
  • Implement robust invoice processing and authorisation procedures.
  • Offer effective payment options and diligently follow up on overdue accounts.
  • Minimise late payments and bad debts through systematic collection efforts.

Good invoicing practices support better cash flow, legal compliance, and professional customer relationships.