Thank you Beachbum, though I am intrigued by the 'spur' tunnel for Queen Victoria. Are you saying that the train would halt in the tunnel to allow the queen to alight? This sounds a bit fanciful given all the difficulties of alighting a railway carriage in the cramped confines of the tunnel. I will investigate further.
I was not expecting to get this opportunity to post a new one as I thought I may be helping someone else towards the ultimate answer. However I do have something which may be of interest. I recently took a balloon flight with Mrs Stewie and being up there looking down gives a wonderful new perspective of the countryside. We passed over this building which looked quite interesting (certainly from above). So where is this?