UK Company Numbers Explained (Companies House)
Every company registered with Companies House is assigned a company number. At first glance it looks like a random identifier — but in reality, company numbers carry useful meaning, especially when prefixes are involved.
Understanding company numbers helps you:
- Identify where a company was registered
- Recognise legal structures at a glance
- Build cleaner and more accurate search filters
- Avoid confusion between similarly named companies
What is a UK company number?
A company number is a unique identifier issued by Companies House when a company is incorporated.
Key properties:
- It never changes, even if the company changes its name
- It remains associated with the company for its entire lifetime
- It is used across filings, accounts, and official records
Because names can be duplicated or changed, the company number is the most reliable identifier for a UK company.
Why company numbers matter for searches
Company numbers are particularly useful when:
- Verifying a specific business
- Avoiding false positives from similar names
- Understanding a company's jurisdiction and structure
- Analysing large datasets or exports
On firmlist, company numbers allow you to:
- Search directly for a known entity
- Segment companies by number prefix (where applicable)
- Validate and de-duplicate lists
Common UK company number formats and prefixes
No prefix (England & Wales)
Format: 8 digits (e.g. 12345678)
These are standard companies registered in England and Wales.
Typical structures
- Private limited companies (LTD)
- Public limited companies (PLC)
Why it matters
Most UK trading companies fall into this category. For broad B2B searches, these numbers dominate.
SC — Scotland
Format: SC + 6 digits (e.g. SC123456)
Meaning
- Company incorporated in Scotland
- Governed by Scottish company law
Why it matters
If your business, service, or regulation differs between jurisdictions, filtering Scottish companies can be essential.
NI — Northern Ireland
Format: NI + 6 digits (e.g. NI123456)
Meaning
- Company incorporated in Northern Ireland
Why it matters
Important for:
- Jurisdiction-specific services
- Public sector or cross-border analysis
OC — Overseas Company
Format: OC + 6 digits
Meaning
- An overseas company registered to operate in the UK
- Incorporated outside the UK but has a UK establishment
Why it matters
Overseas companies may:
- Have different compliance obligations
- Be unsuitable for certain B2B targeting
- Be highly relevant for international or regulatory work
LP — Limited Partnership
Format: LP + 6 digits
Meaning
- A limited partnership
- Different from LLPs
- Often used for investment structures
Why it matters
LPs behave very differently from LTDs and LLPs and are often excluded from standard sales lists.
SO / SL / NC / NL (Other less common prefixes)
Companies House also uses additional prefixes, including:
SO— Scottish OverseasSL— Scottish Limited PartnershipNC— Northern Ireland CompanyNL— Northern Ireland Limited Partnership
These appear far less frequently but can be important for specialist research or compliance work.
LLP and company numbers
Limited Liability Partnerships (LLPs) also have company numbers, but:
- They are not "companies" in the traditional sense
- They are registered and tracked similarly
- Prefixes depend on jurisdiction (e.g.
SOfor Scottish LLPs)
Always pair company number analysis with company type for clarity.
How to use company numbers effectively in firmlist
1. Direct lookup
If you already have a company number, this is the fastest way to find the exact entity.
2. Data validation
Use company numbers to:
- De-duplicate lists
- Match records across datasets
- Validate existing CRM entries
3. Jurisdiction filtering
Prefixes like SC and NI let you:
- Separate Scottish and Northern Irish companies
- Apply region-specific logic
Common mistakes to avoid
Confusing registration location with trading location
A company registered in Scotland may trade primarily in England — company number shows registration, not operating geography.
Ignoring prefixes in analysis
Treating all numbers as equivalent can skew analysis, especially in regulated or public-sector contexts.
Related guides
- Company Types Explained
- Company Status Explained
- SIC Codes Explained
- Postcode & location filtering
- Company age & incorporation date
- Other indicators