How the UK defines SMEs: three very different data problems
The UK government (and Companies House in its own filings guidance) uses the same three-tier classification that originated in EU company law and has been retained in UK statute post-Brexit. The bands are defined by headcount as the primary criterion, with turnover and balance sheet as secondary tests.
Micro businesses are those with fewer than 10 employees. They account for the largest share by number, around 4.2 million firms, but generate a disproportionately small share of commercial B2B spend. Small businesses (10-49 employees) number roughly 220,000 and represent a middle ground where data availability improves considerably. Medium businesses (50-249 employees) number around 37,000 and sit at the top of the SME bracket, with data quality approaching that of large enterprises.
These three groups behave like three entirely separate data markets, not one. A campaign designed to reach Operations Managers at 100-person manufacturing firms in the Midlands is a very different data exercise from reaching sole-trader electricians in Bristol. The common label "SME" papers over that gap.
What Companies House does and does not capture
Companies House is the foundation of any serious UK B2B database. Every limited company (Ltd) and public limited company (PLC), every limited liability partnership (LLP), and certain other incorporated structures must file with Companies House. The active-company count sits at roughly 2 million records, and all of it is public information under the Companies Act 2006.
Each filing includes: registered company name, registered office address, SIC 2007 code (one or more, self-reported at incorporation), incorporation date, accounts type (micro, small, full), and the names of all directors and persons with significant control (PSC). That last point is important. Director names are public record. They are not opt-in data. They are statutory disclosures, and using them for legitimate B2B prospecting falls squarely within the legitimate interests basis under Article 6(1)(f) of UK GDPR.
What Companies House does not contain is contact information. There is no email address, no telephone number, no job title beyond "director" or "secretary." A data supplier adds that layer by cross-referencing corporate websites, public industry directories, and professional listings. Coverage of that enrichment layer is what separates a strong B2B file from a thin one.
The exemptions that shrink the universe
Roughly 3.1 million of the UK's 5.5 million businesses are sole traders. They have no Companies House registration requirement. Neither do general partnerships (two or more people trading without a formal incorporated structure). Together these unincorporated businesses represent a majority of UK business entities by count, but they produce no public statutory filings. The only public signals available are those the business owner has chosen to publish: a website, a Google Business Profile, a listing in a trade directory such as Checkatrade or Rated People, or entries in professional registers like the FCA, SRA, or RICS for regulated occupations.
Coverage from those voluntary sources is uneven. A sole-trader accountant who maintains a website and an FCA register entry is contactable. A sole-trader window cleaner who works entirely by word of mouth and has no web presence is effectively invisible to any purchased data file.
Coverage by size band: what to realistically expect
The table below summarises typical data availability when buying from a quality UK B2B supplier. "Named contact" means a named individual (not just a job title) with at least one verified contact channel.
| Size band | Employee range | Approx. UK count | Companies House record? | Named contact coverage (typical) | Direct email/phone availability |
|---|---|---|---|---|---|
| Sole trader | 0-1 (self-employed) | ~3.1 million | No | 15-35% | Low; often personal email or no email |
| Micro | 1-9 | ~1.1 million incorporated | Yes (if Ltd/LLP) | 30-55% | Moderate; director mobile often available |
| Small | 10-49 | ~220,000 | Yes | 55-75% | Good; business email and direct-dial common |
| Medium | 50-249 | ~37,000 | Yes | 70-85% | Strong; multiple contacts per firm typical |
These ranges are indicative, not guarantees. A supplier with a well-maintained file verified within the last six months will sit at the top of these ranges. One that refreshes annually will drift toward the bottom, because B2B contact data decays at roughly 20-30% per year as people change roles, leave firms, or close businesses.
How SIC codes affect SME targeting quality
The UK SIC 2007 code assigned to a company is self-reported at incorporation and rarely updated, even when the business pivots. For micro-businesses in particular, the registered SIC code is often a poor proxy for what the company actually does. A digital agency that incorporated under SIC 62010 (computer programming) may have shifted entirely to SEO consulting by its third year without ever filing an amendment.
For the small and medium bands, SIC code accuracy is much higher. Firms with employees, accountants, and regular filing obligations tend to keep their classification reasonably current. At the micro end, treat SIC codes as a rough filter rather than a precise taxonomy. A fuller treatment of how SIC codes work in practice is in our guide to UK SIC codes explained.
The practical implication: when building a target universe of micro-businesses, supplement SIC filtering with keyword searches on company name, registered address sector, and director job title. Relying on SIC code alone will both miss firms you want and include firms you do not.
Sector skew: which industries have stronger SME data?
Data quality across UK SMEs is not evenly distributed by industry. Some sectors have structurally higher data availability because firms in them tend to be incorporated, tend to publish contact information publicly, and tend to operate through formal addresses rather than residential ones.
Professional services (accountancy, law, financial advice, consulting) sit at the top. Regulatory registers - the Financial Conduct Authority, Solicitors Regulation Authority, and Institute of Chartered Accountants - publish practitioner-level data that supplements Companies House considerably. A small accountancy practice of four partners is much easier to reach accurately than a four-person landscaping company.
Construction and trades have a mixed picture. Larger firms (25 or more staff) with CHAS, Constructionline, or NHBC accreditation are well-represented. Sole-trader builders and micro subcontractors are not. IT and technology firms, even small ones, tend to have public-facing websites and LinkedIn presences that improve contact coverage. Retail (especially bricks-and-mortar independent retail) and hospitality have high churn rates and lower data quality, because businesses close and reopen under new ownership faster than any file can track.
The B2B data by industry in the UK article covers sector-level availability in more depth for buyers who want to model universe size before buying.
Price implications: why SME data costs more per usable record
Enterprise data (2,000 or more employees) is relatively cheap per record because the universe is small, coverage is high, and each firm has multiple contacts. Micro-business data is the opposite. The universe is large by count but the usable proportion after deduplication, verification, and suppression is much smaller.
A quality file of 1,000 medium SMEs (50-249 staff) with named contacts, verified emails, and mobile numbers might cost in the region of £80-£120 per 1,000. The same nominal 1,000 records of micro-businesses would likely require sourcing 2,000-3,000 raw records to yield 1,000 usable ones after bad-address suppression, deceased-director removal, and TPS washing, which pushes the effective cost per deliverable contact up sharply.
In our experience, campaigns targeting the micro-SME segment produce better results when built around postal and telephone outreach rather than cold email. A one-person business owner checks their mobile every day. Their "business email" is often a Hotmail or Gmail address that sits alongside personal mail, which affects deliverability and attention differently from a corporate domain inbox.
Targeting strategies that actually work for SME outreach
Segment by size band first, then by sector
The most common mistake in SME outreach is treating the whole SME segment as one audience and building one message. A sole trader and a 200-person firm have almost nothing in common in terms of buying authority, budget cycle, or decision-making process. Segment by employee band first. Then apply sector and geography. Then build the message around that specific profile.
Use telemarketing for micro and sole traders
For businesses below 10 staff, telephone is often the highest-performing channel. The owner is the decision-maker, they answer their own phone (or mobile), and there is no procurement process to navigate. Make sure all numbers have been washed against the Telephone Preference Service (TPS) before dialling. Sole traders who have registered personal numbers on TPS must be excluded; the fact that the number is used for business purposes does not override registration on the personal TPS list, a point the Information Commissioner's Office (ICO) has confirmed in enforcement guidance.
Target the small and medium bands by job function
Firms with 10 or more staff start to have functional roles beyond the owner: Finance Manager, Operations Director, IT Manager, Head of Marketing. These job-function titles become targetable for the first time at this size. A software vendor trying to reach Finance Managers across small professional-services firms in the North West can build a tight, relevant list. That kind of precision is not possible at the micro end, where "director" is the only available title for most records.
Combine Companies House identity with enrichment
For the incorporated SME segment, the most reliable approach is to start with a Companies House-anchored identity layer (company name, registration number, registered address, SIC code, director name) and then layer in enriched contact data (email, direct telephone, LinkedIn URL) on top. That two-layer structure means that even if the enriched contact data is stale, the underlying firm identity is accurate. You can verify records, request updates, or use postal as a fallback channel to the registered address.
Compliance note: sole traders and GDPR
Sole traders occupy a grey area under UK data protection law. The ICO treats them as natural persons rather than corporate entities in many contexts, which means the usual B2B legitimate-interests exemption applies less cleanly. Before running a campaign targeting sole traders, complete a Legitimate Interests Assessment (LIA) that specifically addresses why the individual's interest in not receiving your communication does not override your commercial purpose. For electronic communications, PECR consent rules may apply if the contact is on a personal rather than corporate channel. When in doubt, use postal as the safest outreach channel for this segment.