How far is from the airport ?
Depends which airport and time of day- from Heathrow I’d say an hour if you use the express/tube and walk.
It’s about same from City - DLR then underground to Euston or Russell Square
Never done it from Gatwick
Get an answer from Hotel Tavistock staff and past guests.
3 Days in London
Museum Guide for London
London by Foot and Tube