Aérospatiale-BAC , the manufacturer of the aircraft withdrew their support, and the chose not to allow its continued use. As the constructor and holder of the type certificate that makes it legal to fly, they have to be on board for any attempt to bring Concorde back to the air. The problem with this attempt, to appear at the 2012 Olympics in London, is that the most viable airframe would be an ex Air France airframe. In addition to being very expensive, it is doubtful that the French would be willing to let the Roast Bifs fly one of their airplanes over an Olympics that they competed for and lost.
People more knowledgeable that I may disagree, but I think that it would be possible to get the aircraft airworthy again absent the need for this support by Aérospatiale-BAC, but that any help from them is not going to be forthcoming.
Maybe A4's could chime in, he might know someone who accidentally kept some of the paperwork when Braniff was changing Concorde to an N reg and back to proper a English ( G ) bird again.