Using the Companies House API for Lead Generation

Understanding the Companies House API for Lead Generation

If you're involved in B2B sales, marketing, or business development in the UK, you've probably heard about the Companies House API. It's a goldmine of data, but many people don't realise just how powerful it can be for lead generation. The reality is that Companies House publishes information about every registered UK business—roughly 4 million companies at any given time—and this data is freely available through their API.

The trick isn't accessing the data; it's knowing what to do with it once you have it. In this guide, we'll walk through how the Companies House API works, what information you can pull, and the practical considerations you need to think about before building a lead generation system around it.

What Data Does the Companies House API Provide?

Before we talk about using the Companies House API for lead generation, let's be clear about what's actually available. Companies House maintains public records for every limited company, sole trader, and partnership registered in the UK. When you query their API, you get access to several datasets.

Company Registration Data

The core data you'll receive includes company name, registration number, address, incorporation date, and company status (active, dissolved, etc.). This alone is useful for filtering out inactive businesses, but it's just the starting point.

You'll also get filing history, which shows when a company last filed accounts, annual returns, and confirmation statements. If a company hasn't filed anything for years, it's likely inactive or dormant—valuable information for qualifying leads.

Officer Information

Companies House also provides details about officers (directors and secretaries). You get their names, appointment dates, and resignation dates. This is particularly useful for lead generation because it tells you who's actually running the business. However—and this is important—the API doesn't return personal email addresses or phone numbers. That's something you'll need to source separately.

Charge and Filing Data

You can access information about charges (essentially secured loans against company assets) and detailed filing documents. For lead generation purposes, this is less immediately useful, but it can help you understand a company's financial health or growth trajectory.

How to Access the Companies House API

The Companies House API is publicly available and free to use. You'll need to register for an API key on the Companies House website, which takes about five minutes. There are no usage limits in the traditional sense, though they do ask that you don't hammer their servers with thousands of requests per second.

Once you have your API key, you can make requests to endpoints like:

• /company/{company_number} — retrieve details about a specific company
• /search/companies — search for companies by name or other criteria
• /company/{company_number}/officers — get officer information
• /company/{company_number}/filing-history — access filing records

The API returns JSON responses, making it relatively straightforward to parse and store the data in your own database or CRM system.

Using the Companies House API for Lead Generation: The Practical Approach

Now, here's where things get interesting. Using the Companies House API for lead generation is technically possible, but there are some real challenges that people often underestimate.

The Time and Infrastructure Challenge

If you want to build a lead generation system from scratch using the API, you need to think about several things. First, you're talking about millions of records. Processing them all, storing them, and keeping them up to date requires database infrastructure, server capacity, and development time. You'll need to build scripts that run regularly to check for newly registered companies, pull their data, store it, and then enriched it with additional information like phone numbers and email addresses.

For a solo operator or small team, this becomes a significant project. You're not just querying an API; you're building and maintaining a system. Bugs happen. APIs change. Companies House occasionally updates their schema. You'll need to manage all of that.

The Data Enrichment Problem

Here's the critical limitation: the Companies House API gives you company names, addresses, and officer names—but it doesn't give you phone numbers or email addresses for decision-makers. This is by design, for data protection reasons. So if you're planning to use this data for outbound marketing or sales, you need another way to get contact details.

Many businesses build their own enrichment layer by web scraping, purchasing third-party data, or manually researching contact information. All of these approaches have drawbacks. Web scraping is unreliable and may violate terms of service. Third-party data providers can be expensive. Manual research doesn't scale.

Filtering for Quality Leads

Not every registered company is a viable lead. A company might be dormant, dissolved, or simply not relevant to your business. When using the Companies House API for lead generation, you'll want to build filters based on:

• Company status — only active companies
• Company age — newly registered businesses are often higher-intent leads
• Filing activity — recent filings suggest an active business
• Business classification — target specific sectors (e.g., plumbing, electrical work, construction)
• Geographic location — focus on regions where your service is available

The problem is that Companies House classification codes aren't always precise. A business might be registered under a generic code, and you won't know their actual trade until you research them separately.

Building vs. Buying: When to Use the API Yourself

There are legitimate reasons to build your own Companies House API integration. If you're a software company building a B2B product, or if you have very specific, niche lead requirements that no off-the-shelf service covers, then developing your own system makes sense.

However, most businesses don't fall into this category. For marketing agencies, accountants, web designers, and print shops looking to source leads of newly registered trade businesses, building from scratch is often more expensive and time-consuming than it's worth. You're looking at development costs, ongoing maintenance, infrastructure costs, and the time cost of managing a system.

This is where services that automate the Companies House API for lead generation become valuable. They've already solved the infrastructure problem, the enrichment problem, and the filtering problem. You simply receive weekly reports of newly registered companies in your chosen sectors, complete with contact details and social media links—ready to reach out to.

Compliance and Data Protection Considerations

If you do build a system around the Companies House API, you need to be aware of data protection laws. The data from Companies House is publicly available, but once you start collecting, storing, and using it for marketing purposes, you're bound by GDPR and UK data protection regulations.

Key points:

• You need a lawful basis for processing personal data. Public interest or legitimate business interest are possibilities, but they're not automatic.
• You should have a privacy policy explaining what you're doing with the data.
• If you're sending marketing emails, you need to comply with PECR (Privacy and Electronic Communications Regulations), which generally means you need consent first, with some exceptions for B2B cold calling and emails.
• You need to respect unsubscribe requests and keep records.

These aren't just nice-to-haves; they're legal requirements. The ICO (Information Commissioner's Office) takes this seriously, and breaches can result in significant fines.

Practical Example: Targeting Newly Registered Plumbers

Let's say you run a digital marketing agency and you want to target plumbers who've just started their business. Here's how you might approach it using the Companies House API:

1. Query the API for companies incorporated in the last 30 days with SIC codes matching plumbing services (SIC code 4322)
2. Filter for active status and companies with recent filing activity
3. Store the results in your database
4. Enrich the data with phone numbers and email addresses (either through your own research or a data provider)
5. Create a list of prospects and outreach to them with a relevant message about helping new trades establish an online presence

That workflow is theoretically straightforward. In practice, you're writing and debugging code, managing data quality, handling API rate limits, and solving enrichment challenges. Most agencies don't have the technical resources to manage this in-house.

Key Takeaways

The Companies House API is a legitimate and powerful source of business data. It's freely available, regularly updated, and covers every registered UK company. For building a lead generation system, however, there are real technical and operational challenges that shouldn't be underestimated.

The decision to use the Companies House API for lead generation directly comes down to your specific needs and resources. If you have developers on staff and very specific requirements, building your own system might make sense. If you're looking for a reliable, regularly updated list of newly registered trade businesses with contact details included, using a purpose-built service that's already solved these problems is usually more cost-effective.

Either way, understanding how the API works and what data it provides is valuable. You'll make better decisions about your lead generation strategy when you know what's actually available and what the practical limitations are.

If you're interested in exploring how automated lead generation from Companies House data could work for your business, it's worth having a conversation with providers who specialise in this. Most offer trial periods or starter packages so you can see the quality of the data before committing.