A serious answer to this question?
For me, probably scaling down HS Trident 1 (DH 121) to meet the BEA requirement. Boeing were terrified of the original spec Trident 1, as it would've done very nasty things to the 727 (1831 built); instead, BEA insisted on a smaller, less capable aircraft and the result was Trident 1, 2, 3 - a total of 117 built.
S41
That and on the orders of the UK PLC HS travelling to the USA to Boeing in a technology sharing exercise and handing over the all the data on the Trident in what turned out to be a one sided technology sharing deal, this gave the USA the technology to build the curved intake duct for the rear engine that they had thought impossible.... and produce the 727 in the first place.
Handing over the moving tailplane concept data to the USA allowing the Bell X1 to crack the speed of sound, whilst scrapping the Miles M1 that would have and was later proved to have been capable of taking the record, long before the USA.