Ian Jelf wrote:

Not necessarily. You can invoke the little known Great
Northern, Brompton & Piccadilly Historical Set at that
point. **Provided** you don't use "British Museum" on
the Central, Aldwych can double for that, some of its
treasures having been stored on the branch during the war.

I always thought that British Museum was dangerous to play after
invoking GNP&BHS because of the combined ghost station/joined station
paradox when the interchange was built at Holborn!