Understanding SIC Codes: What They Tell You About a UK Company

Every UK company registered with Companies House must declare its nature of business using one or more Standard Industrial Classification (SIC) codes. These five-digit numbers are one of the most overlooked fields in a company profile, yet they reveal a great deal about what a company actually does — and, critically, when what it claims to do does not match what it is registered to do. This guide explains how SIC codes work, what the most common codes mean, and how to use them as a practical risk-screening tool.

What a SIC code actually is

SIC codes are a government-standard classification system that groups businesses by their primary economic activity. When a company is incorporated, the directors declare the nature of the business on Form IN01 using the applicable SIC code, and this code is published on the Companies House register. A company can hold multiple SIC codes — a property developer that also does contracting, for example — but the first listed code is the primary activity.

The system is maintained by the Office for National Statistics and periodically revised. The current scheme (UK SIC 2007) uses five-digit codes in sections ranging from Section A (Agriculture) through to Section S (Activities of households as employers). For commercial screening, the sections you will encounter most often are M (Professional, Scientific and Technical Activities), K (Financial and Insurance Activities), L (Real Estate Activities), and N (Administrative and Support Services).

How to read a SIC code in practice

For practical screening, you do not need to memorise the entire SIC hierarchy. You need to recognise the codes that indicate the type of business you are dealing with, and to spot codes that look incongruent. A supplier that claims to be an engineering consultancy should have a code in the 71 range (Architectural and Engineering Activities). A company whose code is 68100 (Buying and Selling of Own Real Estate) may not be what it appears to be.

Common SIC codes and what they indicate:

• 62011 — Software development. A genuine tech supplier should hold this code.
• 62012 — Web portals. Broadly, digital businesses that are not pure software.
• 68100 — Buying and selling of own real estate. A single-purpose property holding.
• 68320 — Management of real estate on a fee or contract basis. Estate agents and property managers.
• 70100 — Activities of head offices. A holding company or group HQ; may have no operational staff.
• 82990 — Other business support service activities. A broad catch-all used by agencies, consultants and sometimes shell entities.
• 99999 — Dormant company. A company with no current trading activity; may be incorporated for future use or held in reserve.

Using SIC codes as a risk signal

The primary value of SIC codes for procurement and risk teams is cross-checking: does the code on the register match what the company says it does? A company that claims to manufacture electronics but has SIC code 68100 (property dealing) is either using a trading name that does not reflect its registered activity, or the registration is being used as a vehicle for something else. Neither is disqualifying, but both are worth asking about.

More suspicious are: a company with code 99999 (dormant) that claims to be actively supplying goods; a company with multiple unrelated codes that suggests no coherent business; or a company whose only code is 82990 (the broadest catch-all), which often indicates the entity was set up for a single purpose that does not align with its claimed activity.

How to look up a company's SIC code

You can see a company's SIC code on any Companies House mirror, either on the company overview page or in the filing history. The code appears as a line reading "Nature of business (SIC)" followed by one or more five-digit numbers. If you are checking a batch of suppliers, a bulk lookup tool that retrieves the SIC code for a list of company numbers makes the cross-check efficient: you can export the codes, sort them, and quickly isolate any that do not match what your onboarding records say the company does.

Building SIC checks into onboarding

The simplest approach is to add a "nature of business" field to your supplier onboarding form, then compare the stated activity with the Companies House SIC code at the point of first order. A small mismatch (e.g. the supplier describes itself as "consultancy" but the code is 70100, head office) is common and usually benign. A large mismatch (property dealing versus manufacturing) is worth one phone call before you place a large order.

For ongoing monitoring, a quarterly re-check that flags any change in SIC code can alert you when a supplier pivots to a different business — which is not necessarily bad, but means you should re-assess whether it is still the right supplier for you.