Thanks NW1 for your clear and concise answer and for also answering my next question before I had a chance to post it! which was going to be what were the two ledges at the front for? I had always assumed that they were vesitigal canards but in fact they were to help longtiudinal stabilty.
I have another question and that is whenever I see pictures of Concorde's cabin the seat pitch whist not being as tight as economy does seem not to be that generous. So what was the pitch? and if the pitch used in economy on other craft had been used throught the plane could more people have been carried without affecting takoff and landing weights and compromising evacuation etc?
I guess with the length of the flights seat pitch was not an important issue.
Nick