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Getting to grips with HMRC: What UK tax numbers actually mean

Getting to grips with HMRC: What UK tax numbers actually mean

Posted: Tue 29th Jul 2025

8 min read

When you're running a small business, you end up juggling a lot more than you expected – clients, suppliers, late invoices, the odd IT headache… and then there's HMRC.

Somewhere in the pile of tax letters and emails, you'll come across a whole collection of numbers: some with 10 digits, some with letters and others you don't remember applying for in the first place.

They all have a purpose – even if it's not immediately obvious – and knowing what each one means can save you a lot of time when it comes to payroll, tax returns or even applying for a loan.

This brief guide strips it all back. No jargon, no waffle – just a clear explanation of the most common tax identification numbers used in the UK, why they matter and where to find them when you need them.

What do we mean by "tax ID number"?

Unlike in some countries, the UK doesn't have one single tax ID number that covers everything.

Instead, there are several different codes and reference numbers issued either by HMRC or Companies House, depending on what your business does and how it's set up.

Each one has a specific purpose – for example, identifying you as a taxpayer, registering you as an employer or confirming your company is legally incorporated.

Here are the main ones to know about:

  • Unique Taxpayer Reference (UTR) – for dealing with HMRC and submitting tax returns

  • Employer PAYE reference – if you run payroll

  • Company registration number – if you're a limited company

  • National Insurance number (NINo) – used to track individuals' tax and National Insurance contributions (NICs)

  • VAT registration number – needed if you're registered for VAT

Most of these come through automatically when you register with HMRC or Companies House – but knowing what each one is for (and where to find it when you need it) makes life much easier.

The numbers you'll come across – and what they're for

Let's take a closer look at each of the key identifiers.

Unique Taxpayer Reference (UTR)

The UTR is a 10-digit code issued by HMRC. If you're self-employed, in a partnership or running a limited company, this number is tied to your tax account.

You'll need your UTR for:

You'll usually find your UTR in letters from HMRC or in your online Government Gateway account.

Employer PAYE reference

If you employ staff and run payroll, you'll register as an employer with HMRC.

When you do, they'll give you a PAYE reference. It's usually made up of two parts – a three-digit tax office code and a unique reference.

You'll use this number whenever you:

  • submit payroll reports to HMRC

  • deal with tax or student loan deductions

  • include details on payslips, P45s or P60s

It's worth noting that you'll need your PAYE reference if an employee applies for benefits, tax credits or anything that relies on verifying their income.

This number should appear in the welcome pack HMRC sends you when you register as an employer, and on most correspondence related to PAYE.

Company registration number (CRN)

If you've set up your business as a limited company, you'll be issued a CRN when you incorporate via Companies House.

This is your official company ID and appears on your certificate of incorporation.

You'll use it when:

  • filing annual accounts or confirmation statements

  • registering for corporation tax or VAT

  • communicating with HMRC, banks or business partners

The CRN is often listed on a company's website, invoices and official documents. It's not needed for tax returns if you're a sole trader – it's strictly for limited companies.

National Insurance number (NINo)

This one's for individuals rather than businesses, but still important – especially if you're self-employed or employing staff.

The NINo is a personal identifier used by HMRC and the Department for Work and Pensions. You'll need it for:

  • paying National Insurance contributions (NICs)

  • accessing certain benefits

  • student loan deductions and other tax-related matters

You can usually find it on your payslip, P60 or personal tax documents.

VAT registration number

If your business turnover exceeds the current VAT threshold (£90,000), by law you must register for VAT.

When you do, HMRC will issue a VAT registration number – a unique code starting with ‘GB', followed by nine digits.

You use this number when:

  • charging VAT on sales

  • reclaiming VAT on expenses

  • completing your VAT returns

It should appear on your invoices, and your customers or suppliers may also need it.

How to get these numbers

Limited companies

When you register a company with Companies House, you'll be automatically assigned a CRN.

Shortly afterwards, HMRC will send your company a UTR by post. You'll use this to set up corporation tax, VAT and PAYE if needed.

If you're employing staff, you'll need to separately register as an employer via HMRC – that's when you'll be given your PAYE reference.

Sole traders and partnerships

As a sole trader or partnership, you'll need to register with HMRC for Self Assessment. Once you do, they'll issue your UTR.

If you're hiring employees, you'll also register as an employer and get a PAYE reference the same way a limited company would.

Final thoughts

While tax reference numbers aren't the most glamorous part of running a business, they're fundamental to staying on the right side of HMRC.

Each code plays a part in keeping your records straight, your returns accurate and your business compliant.

You don't need to memorise every number, but knowing where they come from, what they're for and where to find them will make your life much easier – especially when deadlines roll around.

So, keep them safe, store them securely and, if in doubt, check your Government Gateway account or get in touch with HMRC directly. It's better than waiting for a penalty letter to jog your memory.

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