Paul wrote:

The disused area looked more like a sub surface than a tube line but may I
guess have been the long disused platform at Aldwych or was there ever a
platform 6 built for the long disused aldwych line tunnel at holborn?

I believe so but didn't it become a private storage facility?

The film makers clearly borrowed from local knowledge as "British museum"
station is not far form Holborn, albeit on the Central Line

More than that - the Central Line platforms were a replacement for British
Museum.