Register for a Companies House API key and base64-encode it as YOUR_API_KEY: for HTTP Basic Auth
GET https://api.company-information.service.gov.uk/company/{company_number}/persons-with-significant-control with Authorization: Basic YOUR_ENCODED_KEY
Parse response.items[] for each PSC; each item includes name, kind ('individual-person-with-significant-control', 'corporate-entity-person-with-significant-control', etc.), natures_of_control[], and notified_on date
For corporate PSCs (kind='corporate-entity-...'), follow the links.self URL to retrieve the corporate entity's details including identification.registration_number and identification.country_registered
Check ceased_on field; only PSCs without ceased_on are currently active controllers
Combine with GET /company/{company_number}/officers for directors and secretaries to build a complete control map
Known gotchas
PSC disclosure is required for UK entities but many overseas entities listed as PSCs provide minimal identification; identification.registration_number is often blank for non-UK corporate controllers
The Public Data API is rate-limited to 600 requests per 5-minute window; exceeding this returns HTTP 429 and requires a 1-minute wait before retrying
Some companies have exemptions (e.g., traded on regulated markets) and will return an 'exemptions' object instead of populated items; handle this case explicitly
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp