Companies House as a prospecting database

Companies House is a free, complete, public register of every limited company in the UK — which makes it the most underused prospecting database in the country. It gives you companies, not contacts: names, ages, size signals, SIC codes and officers, but no email addresses. Used properly, it is the company half of a prospect list; the people half has to come from elsewhere.

What does the register actually contain?

A record for every incorporated entity in the UK: registered name and address, incorporation date, company status (active, dissolved, in liquidation), SIC codes, named officers with appointment dates, and the filing history — including accounts. The accounts category is the quietly useful field: whether a firm files micro-entity, small or full accounts is a rough but honest proxy for size, filed under legal obligation rather than self-reported for marketing. Access is free, the API is free, and bulk data products exist for larger pulls.

In the assembly order described in The B2B Database Building Guide — companies, people, addresses, verification — Companies House is the strongest UK source for stage one. It is complete by law and nobody can opt out of being in it.

What can you filter on — and what should you distrust?

Workable filters: SIC code, incorporation date, geography (registered address, with caveats), company status, and accounts category. The craft is in combining them, because the headline filter is also the least reliable one.

SIC codes are self-reported at incorporation and rarely updated. Plenty of marketing agencies sit under generic "management consultancy" codes; plenty of dormant shells sit under active-sounding ones. So never trust SIC alone. A filter set that works in practice: the SIC codes for your target sub-vertical, and active status, and accounts category consistent with 5–50 staff, and incorporated three or more years ago. Each condition individually is weak; the intersection is a decent shortlist. Registered addresses need one caveat — many firms register at their accountant's office, so geography filters are approximate.

How do you turn the register into a prospect list?

The mechanism, end to end:

1. Translate the sub-vertical into a SIC set. List every code firms in that niche plausibly use, including the generic ones, erring wide at this stage.
2. When the SIC set is drawn, apply the structural filters. Active status, accounts category for your size band, incorporation date, geography. This is where the wide net tightens.
3. When the shortlist exists, sample it by hand. Check 50 companies against their websites; when more than roughly one in ten is a misfit, tighten the filters before proceeding.
4. When the company list is clean, find the people. Officer records name directors, which at small firms often is the decision-maker; confirm current role and function via Sales Navigator.
5. When you have people, enrich and verify. Email addresses come from enrichment tools, and nothing loads into a sending tool unverified.

This pipeline is bounded and repeatable — defined inputs, defined outputs — which is exactly why we deliver it as a fixed-price build rather than an open-ended engagement. Work with edges should be priced with edges; that argument is made in full in why hourly automation billing is a trap.

Where does the register fall short?

Four places. No contact details — ever; it feeds the top of the pipeline, not the sending tool. Trading names — the register knows "XYZ Holdings Ltd", not the brand on the website, so matching to real-world firms takes care. Timing — data is current only to the last filing, so a firm that doubled headcount this year may still look micro. And coverage — sole traders and ordinary partnerships are not on it at all, which matters in some sub-verticals more than others.

Is it legal to prospect from the public record?

Companies House is a statutory public register, and using it to identify companies is uncontroversial. Directors' names are still personal data, so UK GDPR applies once you process them — legitimate interest is the basis commonly relied on for B2B prospecting, and PECR governs the cold email itself: corporate subscribers may be emailed, with identification and an opt-out. Keep a record of where each contact came from. That is a working summary, not legal advice; if in doubt, ask someone qualified to give some.

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