Every limited company in the UK is assigned a company reg number the moment it is incorporated at Companies House. It is a permanent, unique identifier — it never changes, even if the company changes its name, address, or ownership. For anyone running a business, understanding what this number is, where to find it, and why it matters across everything from invoicing to advertising is worth getting right from day one.
Your company reg number is a legal identifier issued by Companies House, and getting to grips with it properly will save you admin headaches — and could also affect how you set up and verify business accounts, including Google Ads.
What Is a Company Reg Number?
A company registration number — often shortened to company reg number or CRN — is an eight-character code assigned to every company registered in England and Wales, Scotland, or Northern Ireland. Companies registered in England and Wales get a purely numerical eight-digit number (for example, 12345678). Scottish companies are prefixed with "SC", and Northern Irish companies with "NI".
This is a definitional fact worth stating clearly: a company reg number is not the same as a VAT number, a UTR (Unique Taxpayer Reference), or a Companies House authentication code. Each of those serves a different purpose, and they are not interchangeable.
The number appears on the public Companies House register and is permanent. If your company changes its trading name, its registered address, or its directors, the company reg number stays exactly the same. That permanence is what makes it useful as an identifier across government and commercial systems.
Where to Find Your Company Reg Number
The most direct route is the Companies House register, which is publicly searchable. Enter your company name and you will see the registration number immediately.
Beyond the register, your company reg number should appear on your certificate of incorporation, which Companies House issues when you first register. If you have mislaid that document, do not worry — the online register is the authoritative source and is available to anyone, free of charge.
In day-to-day business, you are legally required to display your company reg number on all official documents. That includes invoices, letters, emails, your website, and any formal notices. Many businesses overlook this and include it only on invoices, which is a common compliance gap.
Company Reg Number vs VAT Number: The Key Differences
This is one of the most frequently confused points we came across during nine years running a marketing agency. Clients would regularly supply a VAT number when asked for a company reg number, or vice versa. They are entirely different.
| Identifier | Format (UK) | Issued By | Purpose |
|---|---|---|---|
| Company Reg Number | 8 digits (e.g. 12345678) | Companies House | Company identity and incorporation |
| VAT Number | GB + 9 digits (e.g. GB123456789) | HMRC | VAT registration for tax purposes |
| UTR | 10 digits | HMRC | Self-assessment and corporation tax |
| Authentication Code | 6 characters | Companies House | Filing documents online at Companies House |
You can be VAT-registered without being a limited company, and you can be a limited company without being VAT-registered. The company reg number exists independently of your tax status.
For practical purposes, when a supplier, accountant, or advertising platform asks for your "company registration number", they want the Companies House CRN — not your VAT number.
Why the Company Reg Number Matters for Google Ads
This is where the topic connects to something most guides on the company reg number never bother to mention, and it is worth going into properly.
When you set up a Google Ads account for a limited company, or when you attempt to verify your business identity through Google's merchant or advertiser verification process, you will be asked to confirm business details. In some cases — particularly for certain ad categories or when your account flags for review — Google will ask for documentation that includes your company reg number.
Google's advertiser verification programme has become significantly more rigorous. If you are running ads in regulated categories, or if your account is selected for identity verification, having your company reg number readily available and ensuring it matches the details on your Google Ads account speeds up the process considerably. Mismatches between the trading name you use in Google Ads and the legal name on your Companies House record are a common reason verification stalls.
If you want to understand more about how Google Ads account management works at a practical level, the guide on what a Google Ads expert actually does covers the verification and account structure side in detail.
How Business Verification Affects Your Ad Campaigns
Beyond initial setup, business verification has a direct impact on campaign performance in 2026. Google is increasingly restricting the reach of unverified advertisers in competitive categories. If your account is flagged and verification is pending, your ads may stop serving entirely until the process is resolved.
The verification process typically asks for a government-issued document that shows your business name and registration number. For UK limited companies, a Companies House document — either the certificate of incorporation or a recent confirmation statement — is the clearest option. Having your company reg number at hand and cross-referencing it against your Google Ads billing information before verification is requested saves a lot of back-and-forth.
This is the kind of operational detail that becomes obvious once you have managed dozens of accounts. For SMEs running their own ads, it is rarely flagged until there is a problem.
See how Overtime's AI agent handles account-level issues like verification flags so you are not left scrambling when campaigns pause unexpectedly.
Using Your Company Reg Number Across Business Accounts
Your company reg number will come up in more contexts than most business owners expect. Beyond Google Ads verification, it is commonly required when:
- Opening a business bank account (most UK banks require it for limited companies)
- Applying for credit or trade accounts with suppliers
- Registering for government procurement frameworks
- Setting up accounts with advertising networks and data management platforms
In each case, the company reg number acts as the anchor identifier that confirms you are a legitimate incorporated entity. It connects to the public record at Companies House, which any counterparty can verify independently.
For businesses running paid search, having this detail correctly recorded across your ad accounts and billing profiles matters more than most realise. When budget is flowing and campaigns are live, an administrative mismatch is not the kind of thing you want to be resolving under pressure. The guide on how much Google Ads costs for SMEs covers the financial setup side for new advertisers.
Sole Traders and Company Reg Numbers
It is worth addressing a common misconception directly: sole traders do not have a company reg number. If you operate as a sole trader, you are not incorporated, so there is no Companies House record and no CRN.
Sole traders are identified by their UTR for tax purposes and by their personal details for most other purposes. If a platform or supplier asks for your company reg number and you are a sole trader, the honest answer is that you do not have one — and any reputable business will accept that.
The point matters for Google Ads in particular. When a sole trader sets up a Google Ads account, the billing and identity details will reflect the individual rather than a company. That is fine and entirely normal, but it means that during any verification process, the documentation required will differ from that of a limited company.
For a full picture of how paid search management works for small businesses regardless of structure, see the article on Google Pay Per Click management for SMEs.
Where Overtime Comes In
Managing Google Ads properly involves more than knowing your company reg number. Once your account is verified and campaigns are live, the ongoing work — adjusting bids, pausing underperforming keywords, reallocating budget toward what is actually converting — is where most SMEs either overspend or underperform.
Overtime's AI agent handles that ongoing management. It logs into your Google Ads account, analyses performance data, makes adjustments, and sends you a plain-English summary of what changed and why. No agency retainer, no monthly management fee inflating your costs before a single click is bought.
For businesses that have gone through the admin of getting their account set up and verified — including having the company reg number documented correctly — Overtime picks up where that process ends.
To understand the cost side before committing to any management approach, it is worth reading about how Google Ads costs actually break down for SMEs. The numbers are more controllable than most people assume once the account is structured properly.
If you are ready to move beyond ad-hoc management, check what Overtime costs relative to what an agency would charge for the same work — the difference is significant. And once you are running, see how Overtime manages your Google Ads in practice so you know exactly what you are getting.
Before you do any of that, pull up your company reg number on the Companies House register, confirm it matches the business details on your Google Ads billing profile, and make sure it appears on your website footer and invoice templates. It takes ten minutes and removes one of the most common causes of account verification delays.
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Frequently Asked Questions
What is a company reg number and where does it come from?
A company registration number (CRN) is an eight-character identifier assigned by Companies House when a limited company is incorporated in the UK. It is permanent and unique to your company, appearing on the public register and on your certificate of incorporation.
How do I find my company reg number if I have lost my incorporation certificate?
Search the Companies House register at find-and-update.company-information.service.gov.uk using your company name. The register is publicly accessible, free to use, and will display your CRN immediately alongside other registered details.
Why does Google Ads ask for my company reg number?
Google may request business documentation during advertiser identity verification, particularly for accounts in regulated categories or those flagged for review. Your company reg number, shown on Companies House documents, is one of the clearest ways to confirm your company's legal identity and resolve verification requests quickly.
Do sole traders have a company reg number?
No. Sole traders are not incorporated, so Companies House does not issue them a CRN. Sole traders are identified through their UTR (Unique Taxpayer Reference) issued by HMRC, and by personal identification for most account verification purposes.
Should my company reg number appear on my website?
Yes. UK law requires limited companies to display their company reg number on all official correspondence, including websites, emails, and invoices. Failure to do so is a legal compliance issue, not just an administrative oversight.