Every limited company registered in England, Wales, Scotland, or Northern Ireland is assigned a companies house number UK — an eight-character identifier that follows the business for its entire legal life. It appears on invoices, contracts, your website footer, and increasingly, on advertising accounts. If you run Google Ads for your business, knowing where this number fits into your compliance obligations is worth five minutes of your time.
This article explains what a companies house number UK is, where to find it, what you legally need to display, and how it connects to running paid advertising as an SME.
Companies House Number UK: The Core Definition
A companies house number UK is a unique identifier assigned to every company incorporated at Companies House, the UK's registrar of companies. It is not the same as your VAT number, your UTR (Unique Taxpayer Reference), or your HMRC employer reference. Each serves a different function across different parts of government.
The number is permanent. It does not change if you move premises, change directors, rename the company, or restructure. Once assigned at incorporation, it stays with that legal entity until the company is dissolved. This permanence is what makes it the most reliable identifier for a UK business across contracts, credit checks, and regulatory filings.
For companies registered in England and Wales, the number is eight digits (e.g. 12345678). Scottish companies are prefixed with SC (e.g. SC123456). Northern Irish companies carry NI as a prefix. This matters if you are verifying a supplier or checking a company's status before signing a contract.
You can look up any UK company's registration number via the Companies House public register at find-and-update.company-information.service.gov.uk. The register is free, publicly searchable, and updated in near real time as filings are submitted.
Where to Find Your Companies House Number
If you incorporated your company yourself, the number appears on your certificate of incorporation, which Companies House issues digitally. It also appears on the confirmation statement your company files annually, on the top of your company's public filing history, and in the welcome email from Companies House at the point of registration.
If you used a formation agent or accountant to incorporate, they will have this on file. It takes thirty seconds to retrieve: search your company name on the Companies House public register and the number sits at the top of the company record.
For companies registered in Scotland or Northern Ireland, the same process applies through the central register — there is no separate Scottish or Northern Irish database to navigate.
What You Must Display by Law
Under the Companies Act 2006, UK limited companies are legally required to display their companies house number UK on all business letters, order forms, and their website. The requirement also extends to emails that could reasonably be described as business correspondence. The number must appear alongside the registered company name and registered office address.
Many SMEs miss this. When we ran our marketing agency, we regularly encountered clients whose websites were technically non-compliant because a developer had stripped out the footer during a redesign. The fine for non-disclosure is a civil penalty, and while enforcement is inconsistent, the risk is unnecessary when the fix takes two minutes.
The display obligation applies regardless of trading name. If your registered company name is Acme Holdings Ltd but you trade as Bright Ideas Marketing, your correspondence must carry the registered name and the companies house number UK, not just the trading name.
For a broader look at how company registration intersects with day-to-day business administration, this guide on Company House Number for SMEs covers the practical compliance angle in more detail. If you also need to contact Companies House directly, this walkthrough on calling Companies House explains the process clearly.
How This Connects to Google Ads
This is where it gets relevant for anyone running paid search. When you set up a Google Ads account for a UK business, you are entering into a legal and financial relationship with Google. Google does not currently require your companies house number UK at the account creation stage, but it does require accurate business information — legal name, registered address, and billing details — that should match your Companies House record.
Mismatches between your trading name in Google Ads and your legal entity details can cause problems during ad verification, particularly since Google rolled out its advertiser verification programme. Under this programme, Google may ask you to verify your identity and your business's legal existence. Having your companies house number UK to hand speeds up this process considerably.
| Document / System | Requires Registration Number? | Notes |
|---|---|---|
| Companies House public register | Assigned automatically | Permanent and public |
| Google Ads account setup | Not mandatory at setup | Required if verification is triggered |
| Business bank account | Yes, for limited companies | Required at account opening |
| HMRC Corporation Tax registration | Cross-referenced | Linked but separate from UTR |
| Business invoices and letters | Yes, legally required | Companies Act 2006 obligation |
| Website footer | Yes, legally required | Applies to all UK limited companies |
Running paid advertising without having your compliance fundamentals sorted is a common SME oversight. It does not break your ads, but it creates legal exposure that is entirely avoidable. If you are still getting to grips with how paid search works as a channel, What Is Paid Search: The SME Guide is a useful starting point before you commit serious budget.
Google Advertiser Verification and Business Identity
Since 2021, Google has been progressively rolling out advertiser identity verification across markets. In the UK, this process requires advertisers to confirm who they are and what they are promoting. For limited companies, your companies house number UK is one of the most efficient ways to confirm legal existence without lengthy document uploads.
The verification process typically asks for a government-issued document or business registration evidence. A screenshot of your Companies House record — showing your registration number, registered address, and incorporation date — satisfies this requirement cleanly. This is an operational detail that tends to get missed in generic Google Ads guides but matters significantly when verification is triggered at scale.
Verification failures delay campaigns. We saw this repeatedly with clients whose accounts were flagged during the rollout period — accounts that had been running for years suddenly required documentation that nobody had thought to keep accessible.
For SMEs managing Google Ads in 2026, the administrative baseline has quietly risen. Knowing your registration details, keeping your business information consistent across accounts, and maintaining compliance with display obligations is no longer optional hygiene — it is table stakes for uninterrupted advertising.
See how Overtime approaches Google Ads management for SMEs if you want to understand what active, ongoing account management actually looks like in practice.
Running Ads as a Registered UK Company
Once your compliance foundations are in place, the question shifts from administration to performance. Many SMEs set up their Google Ads account once, correctly, and then leave it largely untouched — which is where the real money gets wasted.
Paid search management for a registered UK business involves more than account setup. It involves continuous bid adjustment, negative keyword management, budget reallocation based on performance data, and pausing ad groups that are spending without converting. For a detailed look at what that management actually costs and what it covers, Google Pay Per Click Management: What SMEs Need to Know breaks it down clearly. And if you want to understand what you are likely to spend before committing, How Much Is Google Ads for SMEs gives realistic figures.
The gap between a well-managed account and a neglected one compounds quickly. A registered limited company spending £1,500 per month on Google Ads without active management is typically losing a meaningful percentage of that to wasted spend on irrelevant searches, stale bids, and underperforming ad copy. The registration number is the administrative starting point; what happens inside the account after that determines whether the spend is worthwhile.
Review Overtime's pricing for SME Google Ads management to see what active management looks like at different budget levels.
What Overtime Does With Your Account
Overtime is an AI agent that manages Google Ads accounts for SMEs directly — logging into accounts, adjusting bids, pausing underperforming keywords, reallocating budget toward what is converting, and sending plain-English summaries of what changed and why.
It is not a set-and-forget scheduler. It operates with the same active logic a human account manager applies: monitoring performance, identifying inefficiency, and taking action. The difference is that it does this continuously, without the overhead of an agency retainer or the lag of a weekly check-in.
For a registered UK company running paid search, the combination matters: get your companies house number UK and legal compliance sorted once, then focus energy on the performance layer. That is where the return actually comes from.
If you are exploring how AI-driven management compares to traditional agency models, Best PPC Agency or AI Agent: What SMEs Need covers the trade-offs honestly, including where each approach falls short. For a broader view of what ongoing paid search management should deliver, Paid Search Management Service: What SMEs Actually Get is worth reading alongside it.
See what Overtime does inside a Google Ads account before making any decisions about how you manage paid search going forward.
If you are setting up or auditing your Google Ads account this week, start with your companies house number UK — confirm it appears correctly in your business information, check your website footer is compliant, and verify that your legal trading name matches what appears in your Google Ads account. These are five-minute tasks that prevent much larger problems later.
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Frequently Asked Questions
What is a companies house number UK and where do I find it?
A companies house number UK is a unique identifier assigned to every company incorporated at Companies House. It appears on your certificate of incorporation, your annual confirmation statement, and on your company's public record at the Companies House register, which is free to search.
How many times must the companies house number UK appear on my website?
There is no specific count required, but it must be clearly visible on your website — typically in the footer — alongside your registered company name and registered office address. This is a legal requirement under the Companies Act 2006 and applies to all UK limited companies.
Do I need my companies house number to run Google Ads?
Google does not ask for it at account setup, but it becomes relevant if your account is selected for advertiser identity verification. Having your registration number and a copy of your Companies House record available speeds up verification and prevents campaign delays.
What is the difference between a companies house number and a VAT number?
They are entirely separate identifiers. Your companies house number UK is issued by Companies House at incorporation and relates to your legal entity. Your VAT number is issued by HMRC when you register for VAT and is only required if your turnover exceeds the VAT threshold or you register voluntarily.
Should I display my companies house number on business emails?
Yes. The Companies Act 2006 requires it on business letters and order forms, and HMRC guidance extends this to emails that constitute business correspondence. Including it in your email footer alongside your registered address is the simplest way to stay compliant.