That's co-operation between two manufacturers, which is also what led to the similarity between the front end of the Caravelle and the Comet. What I meant was co-operation between the certifying authorities of the UK and France, as you would need the French CAA signing off on a type rating for an aircraft that had not been type certificated by them, and may not have been flown by them. Vice versa for the UK providing a Caravelle rating on a UK licence based on a Comet rating. It's an interesting idea, but from a flight characteristics and cockpit layout perspective, as well as from a legal perspective, it was not possible in those days.