Nine Very Important Codes Everyone Loses And How To Find Them
It's a conversation we have almost every week.
“Do you know your UTR number?”
"What’s a UTR number?"
Whether you're self-employed, a landlord, a company director or an employer, there are a surprising number of reference numbers, codes and IDs linked to your taxes and business affairs. The problem is that most of them arrive once, get filed away (or thrown away), and then become impossible to find when you actually need them.
Here's a guide to the most common numbers we ask our clients for, what they look like, where they come from, and what to do if they've gone missing.
1. UTR (Unique Taxpayer Reference)
What is it?
Your UTR is the reference number HMRC uses to identify you for Self Assessment.
If you're self-employed, a landlord, a partnership member or someone who completes a tax return, you'll almost certainly have one.
What does it look like?
10 digits only
Example:
1234567890
How does it arrive?
Usually by letter from HMRC when you first register for Self Assessment.
You'll also find it on:
Tax returns
HMRC statements
Notices to complete a tax return
Self Assessment correspondence
Lost it?
You can often find it by:
Logging into your Personal Tax Account
Checking previous HMRC letters
Contacting HMRC
Your accountant may also have it if you've provided it previously.
2. National Insurance Number (NI Number)
What is it?
Your National Insurance number links your tax, National Insurance contributions, state pension record and employment history.
What does it look like?
Two letters, six numbers and a final letter
Example:
AB 12 34 56 C
How does it arrive?
Historically as part of your National Insurance registration.
It can often be found on:
Payslips
P60s
HMRC letters
The HMRC app
Your Personal Tax Account
Lost it?
You can:
Check a payslip or P60
Log into your Personal Tax Account
Use HMRC's online service to retrieve it
3. Government Gateway User ID
What is it?
This is your HMRC online login ID.
It's different from:
Your National Insurance number
Your UTR
Your VAT number
What does it look like?
Usually 12 digits, although older ones can differ slightly.
Example:
123456789012
How does it arrive?
It's created when you set up an HMRC online account.
You'll usually see it:
On screen when registering
In HMRC registration emails
Within your online account details
Lost it?
HMRC has an online recovery service that can usually retrieve your Government Gateway ID using details they already hold.
4. VAT Registration Number
What is it?
Your VAT registration number identifies your business for VAT purposes.
You'll need it for:
VAT returns
Invoices
Supplier checks
VAT registrations with software providers
What does it look like?
Usually:
GB123456789
or simply
123456789
How does it arrive?
On your VAT registration confirmation from HMRC.
You'll also find it on:
VAT certificates
Submitted VAT returns
Business invoices
Lost it?
Check:
An invoice you've issued
Your bookkeeping software
VAT correspondence from HMRC
5. Company Authentication Code (CAC)
What is it?
A six-character code issued by Companies House. It allows documents to be filed online for a company and is often needed by accountants when taking over a company or filing certain forms electronically.
What does it look like?
Six characters, usually a mixture of letters and numbers.
e.g. A1B2C3
How does it arrive?
Usually issued by Companies House when a company is incorporated, or sent separately if requested.
Lost it?
It can be requested from Companies House and sent to the registered office.
6. Employer PAYE Reference Number
What is it?
An employer reference used for payroll.
What does it look like?
Usually:
123/AB456
How does it arrive?
When you register as an employer with HMRC.
Lost it?
Check:
Payroll software
HMRC employer letters
RTI submissions
7. Accounts Office Reference Number
What is it?
Used when paying PAYE and National Insurance to HMRC.
What does it look like?
Usually:
123PA12345678
How does it arrive?
Alongside your PAYE registration details.
Lost it?
Check:
HMRC employer correspondence
Payroll software
Previous payment records
8. Company Registration Number (CRN)
What is it?
Your company's official registration number at Companies House.
What does it look like?
Usually 8 digits.
Example:
12345678
Some company registration numbers contain letters, particularly companies registered in Scotland, Northern Ireland or under certain Companies House registration types.
How does it arrive?
When the company is incorporated.
Lost it?
Search your company on the Companies House website and you'll find it instantly.
9. Pension Scheme Reference Numbers
What are they?
These identify workplace pension schemes and employer registrations.
What do they look like?
The format varies between providers.
How do they arrive?
Usually through pension provider correspondence.
Lost them?
Contact the pension provider directly or check previous scheme documentation.
Our Advice? Keep Every HMRC Letter
In a world where most things are digital, it's surprisingly common for important tax details to arrive by post.
Even if a letter doesn't seem important at the time, it could contain a reference number you'll desperately need a year later.
A simple folder labelled "HMRC" (physical or digital) can save hours of frustration.
And if you're not sure what a letter means or whether it's important, send it to us. We'd much rather answer a quick question today than spend three weeks tracking down a missing reference number later.