It's only 70 years old, it should be on plans of the building or someone probably remembers it...
> it should be on plans of the building
But it wasn't.
> The team was at the Historic England Archive poring over some 10,000 uncatalogued documents relating to the palace when they found something interesting: plans for a doorway in the cloister behind Westminster Hall.
> Back at the palace, they found that tiny keyhole in the wood paneling — just where the plan suggested it would be.