Many people refer to a “UK tax number,” but in practice the UK does not operate a single, universal tax identification number.
Instead, different tax references apply depending on whether you are an individual, an employer, or a business, and on what tax obligations you have.
This article explains, in a clear and structured way, the main tax-related numbers used in the UK, what each one is for, and who needs them.
1. National Insurance Number (NI Number)
Purpose
The National Insurance Number is the most commonly used personal tax-related identifier in the UK.
Used for
- Employment
- National Insurance contributions
- State pension and benefits
- Personal tax records linked to work income
Who needs it
- Individuals working in the UK
- Self-employed individuals
Format
Typically two letters, six numbers, and one final letter (e.g. AB123456C)
Key points
- Issued once and remains the same for life
- Not a tax filing reference
- Having an NI number does not automatically mean you are registered for Self Assessment
2. Unique Taxpayer Reference (UTR)
Purpose
The UTR is the primary reference number for filing tax returns.
Used for
- Self Assessment tax returns
- Declaring self-employment income
- Rental income
- Company tax filings
- Communication with HM Revenue & Customs
Who needs it
- Self-employed individuals
- Landlords
- Company directors
- Limited companies
Format
Usually a 10-digit number
Key points
- Individuals and companies each have their own UTR
- Many people have an NI number but do not have a UTR until they are required to file a tax return
- This is the number most commonly meant when people say “tax number”
3. PAYE Reference Number
Purpose
This is the tax reference used by employers under the Pay As You Earn (PAYE) system.
Used for
- Paying salaries
- Deducting income tax and National Insurance from employees
- Reporting payroll information to HMRC
Who needs it
- Companies with employees
- Company directors who pay themselves a salary
Format
Typically a combination such as 123/AB45678
Key points
- This is a business/employer reference, not a personal tax number
- A company may have a PAYE reference even if it has only one employee
4. VAT Number
Purpose
A VAT number identifies a business registered for Value Added Tax.
Used for
- VAT returns
- Issuing VAT invoices
- Charging and reclaiming VAT
Who needs it
- Businesses with taxable turnover above the VAT threshold
- Businesses that voluntarily register for VAT
Format
Usually starts with “GB” followed by nine digits
Key points
- Not all businesses have a VAT number
- A VAT number is separate from corporation tax and PAYE references
5. Company Registration Number (CRN)
Purpose
The Company Registration Number identifies a company registered at Companies House.
Used for
- Company identity
- Legal filings
- Banking and commercial contracts
Who needs it
- All UK limited companies
Key points
- This is not a tax number
- It cannot be used for tax filing or communication with HMRC
Summary Table
| Reference | Is it a tax number? | Who uses it | Main purpose |
|---|---|---|---|
| NI Number | Yes | Individuals | Employment and National Insurance |
| UTR | Yes | Individuals and companies | Tax returns |
| PAYE Reference | Yes | Employers | Payroll and salary reporting |
| VAT Number | Yes | VAT-registered businesses | VAT reporting |
| Company Registration Number | No | Companies | Company identification |
Common Misunderstandings
- Assuming an NI number is the same as a tax filing reference
- Believing a company registration number is a tax number
- Thinking one person or business has only one tax reference
- Assuming no action is required until HMRC contacts you
In practice, many penalties arise not from deliberate non-compliance, but from using the wrong reference or failing to register for the correct one.
Professional Note
In the UK tax system, using the correct reference for the correct obligation is essential.
Problems often arise where:
- A UTR is required but has not been obtained
- PAYE or VAT registration is triggered but not completed
- Tax correspondence is misunderstood or ignored
If you are unsure which tax references apply to your situation, early clarification can prevent unnecessary penalties and investigations.
