Registries & filings
UK Companies House
Free UK company data including full filing history, accounts, officers and persons with significant control.
Almost every Crown Dependencies structure touches a UK entity somewhere. This is where the free financial detail actually lives.
Worth reaching for early even when your subject is an island entity. UK filings are far more generous than the islands’ (accounts, charges, officer histories and PSC data are all free), and a UK subsidiary, parent or corporate director will often tell you what the local register will not.
The API is free and well documented if you need to work at volume.