I was also able to fly to Westwood, where the underground factory was. The photo loses resolution in the place where the entrance to the underground factory was, but all those little bungalows one sees at the bottom were especially made to house the workers of the Royal Enfield factory. They were painted in red, apparently, and were visited by Queen Mary in 1943 in a morale boosting tour. Today there are neighborhoods there, but the red houses are long gone. The entrance to the underground factory is just North of that yellow square is, an area not well covered by the 1945 photo.
Unfortunately the 1945 photos do not extend to Bradford-on-Avon, it would have been nice to see the factory there that has been torn down by now. Finally, I went to 48 Holborn Viaduct, where the London Royal Enfield Depot was. Today it is a parking lot, but in 1945 one sees a building there,