The 3 engine concept was a British invention in the De Havilland 121. DH thought there might be technical cooperation with Boeing and invited some of their designers over to examine the idea. They then waited for the return invitation - which never came.
Meantime BEA panicked in the 1958 recession and cut the spec to suit the average BEA sector - result Trident.
And suddenly there was this 727 bearing a remarkable resemblance to the DH121!
Having said that, the Trident was one of the finest bad weather flying machines it has ever been my good fortune to fly - and did most of the CAT III early developement.