The Red Flag Alert API provides advanced search capabilities and access to detailed information on millions of UK businesses. With full integration into the Companies House filing history document API, PDFs of submitted documentation can also be obtained from one easy point.
This documentation site provides an introduction on how to use it and details of its capabilities.
At this present time, the current version of the API is v4. As new features are added, any that have the potential to break backwards compatibility will always be introduced on a new version number of the API, leaving the existing API version untouched.
However, any new features introduced in this way will only be available in the new version of the API, i.e. version v5.