UK Company Number Format: Prefixes and Leading Zeros

A UK company number is always eight characters.

If yours looks like six, you have dropped two zeros, and that is why the form keeps rejecting it.

The short answer

Three rules that cover almost every case:

1. Always eight characters. Digits, or two letters plus six digits.
2. Leading zeros are part of the number. 00000006 is not 6.
3. The number never changes. Not when you change name, not when you move address, not when you change directors.

Why the leading zeros trip everyone up

Companies House issued numbers sequentially from the beginning, so the earliest companies have very low numbers padded out to eight digits.

The problem is that spreadsheets and databases treat the number as numeric and strip the padding:

• You export a list, 00123456 becomes 123456
• You paste it into a bank form, the form rejects it
• You search the register with the short version and find nothing

The fix is to treat the company number as text, never as a number. It is an identifier that happens to be made of digits, not a quantity.

If a UK company number you have been given is shorter than eight characters and has no letter prefix, pad it with zeros on the left until it reaches eight. That is almost always the correct number.

What each prefix means

The two-letter prefixes are not decoration. They tell you both where the entity is registered and what type it is.

The practical reading, if someone hands you a number:

• Starts with OC, SO or NC → it is an LLP, not a limited company. Different accounts, different members, no shares
• Starts with LP, SL or NL → it is a limited partnership. Different again
• Starts with BR → you are looking at a branch of a foreign company, not a UK company
• Starts with SC or NI → a UK company, but registered in a different UK jurisdiction

That last point matters more than people expect. Scotland has its own legal system. A Scottish company is a UK company, but the law applying to it is not identical.

England and Wales company

012345678 digits, no prefix. The leading zero is part of the number

Scottish company

SCRegistered in Scotland, which has its own legal system

1234566 digits

Limited liability partnership

OCAn LLP, not a limited company: members, not shares

1234566 digits

UK establishment of an overseas company

BRA branch of a foreign company, not a UK company at all

1234566 digits

SO and NC are LLPs too; LP, SL and NL are limited partnerships; FC, SF and NF are overseas companies.

Where to find your company number

In order of reliability:

1. The certificate of incorporation. It is on the face of the document
2. Any filing acknowledgement from Companies House
3. Your company's own letterhead, where it is legally required to appear
4. The public register, which is free

And a legal obligation people forget: a UK company must display its registered name, company number, place of registration and registered office address on its business letters, order forms and website. If your website does not show the company number, you are non-compliant, quietly.

Numbers that are not your company number

UK companies accumulate identifiers, and they are routinely confused with each other.

A form asking for your "company registration number" wants the Companies House number. A form asking for your "tax reference" almost certainly does not.

What happens to the number over time

The number is permanent, and that is deliberate.

• Change of name — number unchanged. The register shows the previous names
• Change of registered office — number unchanged, even moving between English and Welsh addresses
• Re-registration from private to public, or the reverse — number unchanged
• Dissolution — the number is retired with the company, and not reissued
• Restoration after strike-off — the company comes back with the same number

The only situation that produces a new number is forming a genuinely new company. If a supplier's company number changed, you are dealing with a different legal entity, whatever the name suggests.

When the number does not find the company

Four causes, in order of likelihood:

1. Leading zeros stripped. Pad to eight and try again
2. Prefix omitted. 123456 for a Scottish company will not resolve; it needs SC123456
3. The letter O and the digit 0 swapped. OC is the letter O; the rest is numeric
4. The company was dissolved. Dissolved companies stay on the register, but some search filters exclude them by default

If you are working out what a UK company must display and file once it exists, that sits alongside the other running obligations worth seeing set out together.

The summary