That's Pegasus house, which was not the original HQ of the Bristol aeroplane company as that's the grade one listed building on the other side of Pegasus house, behind the set of gates. Pegasus house was built in the 1920's / 1930's and became the HQ / drawing office of the Bristol Aeroplane company. The building is itself grade 2 listed I believe as it has many Art Deco / Art Nuvelle features including a fantastic stain glass window which runs the full height of the building by the main stair case. The directors offices and boardroom also feature wood paneling and a mix of 1950's / 1960's office architecture with appropriate decoration and bright colour schemes !. The building was latterly used as storage for numerous company documents and office furniture.
Hope this helps
Best regards
W.G