Companies House API Alternative, When the Official API Isn't Enough for Lead Generation

If you've ever tried to build a UK B2B prospect list straight from the Companies House API, you've probably hit the same wall everyone else does: it's rate-limited (600 requests / 5 minutes), returns only registry data (no websites, no emails, no phones), and has no concept of "find me companies similar to this one." It was built for compliance lookups, not lead generation.

That doesn't mean the API is bad, it just means it's not the right tool if your goal is to get a clean, enriched prospect list this week. This post walks through what the official Companies House API actually gives you, what it doesn't, and what your options are when you need more.

What the official Companies House API gives you

The free Companies House API returns the public register data: company name, number, status, registered office, SIC codes, incorporation date, officers, and filing history. That's the same data you'd see on the Companies House website, but in JSON instead of HTML.

For most UK lead generation use cases, this is your *starting point*, the registry is the canonical UK business list. But there are three things it deliberately doesn't do:

1. It returns no contact data

There's no email address, phone number, or website on a Companies House record. The registered office is a postal address, often the company accountant's office, not where the business actually operates. Officers have names but no contact info beyond what's already public.

2. It's rate-limited

600 requests per 5 minutes is fine for compliance lookups but useless if you're trying to scan tens of thousands of companies. Bulk data files exist as a workaround, but those land as 1-million-row CSVs that you have to parse and filter yourself.

3. It has no advanced search

You can't ask "show me companies in SIC 41201 that incorporated in the last 90 days in the SE postcode area." The advanced-search endpoint supports a small number of fields and doesn't compose well. Most prospecting filters require pulling the bulk data and querying locally.

When DIY is the right answer

If your team has engineering capacity and your prospect list is one-time or rarely refreshed, DIY against the API or bulk files can work. The pattern is:

1. Pull the monthly bulk file from Companies House (free). 2. Load it into Postgres or BigQuery. 3. Filter by SIC + region + age. 4. Hand-enrich the resulting list with websites and emails (Google Maps API, manual research, or a separate enrichment vendor). 5. Re-run quarterly when fresh data drops.

Total time to first usable list: ~2 weeks of engineering, ongoing maintenance cost.

When you want a tool instead

If your prospecting is list-based and recurring (you want fresh leads every week or month, filtered the same way), DIY rapidly turns into a part-time job. That's where a tool like Leadistry saves time:

• Mirrors the entire UK Companies House register so search is instant.
• Adds the SIC code filtering the official API doesn't support natively.
• Runs the enrichment pipeline (website, email, phone, LinkedIn) automatically.
• Refreshes weekly without you touching anything.
• Per-user dedup so each run only delivers companies you haven't seen.

For a UK accountant looking for newly-incorporated companies, an insurance broker tracking active charges, or a recruiter monitoring recent director changes, the tool route is dramatically faster than DIY.

How to decide

Quick decision tree:

• One-off list, no recurring need, have engineering → DIY against the API or bulk files.
• Recurring list, no engineering bandwidth → Use a tool. Leadistry's free trial is 6 leads, no card.
• High-volume + custom enrichment requirements → DIY for the registry side, plus an enrichment vendor for contacts.

The Companies House API is excellent for what it was designed to do. It just wasn't designed for prospecting. Knowing that up front saves you a few wasted weeks.