Bahrain’s royal family has built up vast private wealth, including a $900m portfolio of UK real estate, after embarking on controversial development projects built on disputed land in the Gulf kingdom.

The revelations, which are based on company records, give a rare insight into the closely guarded wealth and investment strategies of the Bahraini royal family while it is under scrutiny over its crackdown on protests.

A Financial Times investigation has found that in the past decade Premier Group, the secretive private investment vehicle believed to be owned by the king and members of his family, became the owner of undersea plots that the company used to obtain stakes in land reclamation joint ventures to build luxury hotels, office buildings and housing. Premier Group subsidiaries have shares in projects — including some of the island’s showcase developments — with an investment value of at least $22bn and the potential to net billions.