I'm aware of a 1942 agreement between the US and UK dividing efforts towards transports (US) and bombers (UK)
There was no US veto on UK airliners: this is a misreading of Lend/Lease Act requirement that recipients not copy or sell US supplies. Priority in production was agreed as bombers/UK, transports/US. This was not to inhibit new US bombers, nor to impede Cabinet Committee on Reconstruction Problems from examining airliners. War Cabinet Minutes W.M.(43).35, 25/2/43, SecState for Air approving spend on Brabazon Types: “We will not accept a solution (to Civil Air Transport) on the basis that we won’t build any a/c and we want authority (to) plan some production” (allocation of strategic materials was prioritised, 1941-45, by a Joint US/UK Committee in light of military exigency).
UK Aero has been superb at spin, to obscure the true causes of its shortcomings - which were that, commercially, it was hotbed of cold feet, expecting the State to fund its R&D and provide its markets.(Beaverbrook, attributed to (Sir)Peter Masefield by Nahum,P.30 in R.Bud/P.Gummett,Cold War,Hot Science,Harwood,1999.)