Company Number Format and Suffixed Letters


Thanks to various sites and official documentation, I had the understanding a UK Company (Registration) Number could be one of the three following formats.

  • 8 numbers, 00000000
  • 1 letter prefix followed by 7 numbers, A0000000
  • 2 letter prefix followed by 6 numbers, AA000000

Recently, we’ve had a company come to us with the format AA00000A, and I’m unable to find documentation covering this single letter suffix format anywhere.

Folks are often pointed to the Uniform Resource Identifiers Customer Guide PDF which also, does not specify that this is a valid format. I found an HMRC document which lists some prefixes not described in the URI doc, but again, no suffixes. Having a quick look through the Companies House github hasn’t shone any light on this format either.

The only breadcrumb I’ve tracked down is from a github post for UK Company Number regex which suggests that the one letter suffix can be C,D,F,L or R.

Can you share the details of this format, and any other variations please?

This is an old link and I don’t know how up to date it is, but this is a list of prefixes where CH does not hold the records for these types of companies: Exclusions from the Company Register

I think the bullet pointed formats you have here only apply to companies formed at Companies House and other organisations use their own 8 character format (which tend to be similar).You might need to look to the organisation responsible for the registration/registers for these companies to find out what suffixes are possible and what they mean as the system they use is not maintained by Companies House.

The majority of them are probably going to be various mutual societies maintained by the FCA. They have a list of suffixes in the lower half of their glossary here: Mutuals Public Register: Glossary

These include some of the single letter ones above: (C = Credit Union etc).

These will tend to have an IP, SP or NP preffix for England/Wales, Scotland and NI respectively. For the different regions you’d have to find the equivilent page, for example I think Scottish societies tend to have a two letter suffix as well, with the first being S so a Scottish Credit Union would be SPXXXXSC or something like that.

To make it more complicated the laws around all of this have changed over time so you can find the occasional anomoly that none of this applies to, which may need some detective work. eg: GARDEN HOUSE NURSERY (THE) overview - Find and update company information - GOV.UK SL is a Scottish limited partnership, but I have no idea what the A means on the end of it!


I was unaware other bodies had agency over this identifier, I had hoped there would be a universal document somewhere to cover all formats but it sounds like that’s unlikely.

Thanks for the info, very useful.