The first purpose built aircraft factory in Britain was built in Hendon to house the Grahame-White Aircraft company. Parts of it were moved and reassembled by the Museum as a place to keep a collection of planes from World War one and before. Mr Monkey went through a little door and found a collection including a Blériot, a Caudron G3, and several different types of Sopwith.
There's a full list of the planes in the Grahame-White factory at the Grahame-White Factory Collection website.
Copyright Rik Shepherd and Mr Monkey.