Before the signing of the treaty, BAC and Sud-Aviation had agreed in principle on how the work of developing and producing the airframe of the supersonic airliner should be shared between them. One of the companies' first tasks now was to convert this general understanding into a definitive agreement. They had to produce an acceptable and practical plan for enabling the design and production work to be broken down and allocated, on a 60-40 split to France and Britain. It took long meetings and much hard bargaining to agree on a manufacturing break-down but, in general, the division of responsibilities then formulated still holds good today.
The airframe work was divided 60-40 in favour of France because the balance of work on the engine was weighted in favour of Britain. By November, 1962, the engine selected for the Concorde, the supersonic version of the Bristol-Siddeley Olympus, was already being developed. Engines were in existence and running on the test-bed, and whatever adjustments might be made in the new programme to allow joint AngloFrench development of the Olympus 593, the British work content would be greater than the French.
I was really tempted to vote Spitfire..... but gave Concorde the nod because of its beauty and the fact that it was decades ahead of its time. It was unique and there will probably never be anything else quite like it.