Been looking at some modern aeriel shots. Looks like the hangar structure apart from the cladding is still original with a new late 1960's frontage added as the V shape roofs are retained further back. The 45 degree support beam coming out of the roof edge half way along it would support my view, which can just be seen in one of the photos from vintage ATCO
Even this recent photo has seen changes with the removal of the Britannia ops building and the original wooden terminal on the extreme middle right of the photo.
origin of photo unknown