pb: I like that: it's better than the implication that Burke/Dobson mishandled a negotiation, or that Boeing intended/and HSAL succumbed to deception - lifting UK "secrets". Cast our minds back to the way we were as 1959 unfolded. BEAC's passengers had only gained access to any real money in 1958 - previously, currency controls had been rigid, to serve businessmen hunting exports. We were then granted £50 p.person p.a - transactions entered in your passport. All BEAC's routes were a) monopoly protected - poor souls like Dan could only fly where BEAC chose not to go, like Lux; and b) revenue-pooled with the reciprocal carrier, say AF. Cosy cartel, no competition, in service, frequency or fare. So, Spey-size would do fine, even seen as capacity-at-risk.
Now, compare and contrast with US domestic: capacity/frequency is King. Clearly, Medway-size. So Pratt invented JT8D just at Boeing Board 727 Project Launch. RR could not/would not credibly do Spey+Medway concurrently, so settled for the safely-funded BEAC job...and were evermore disdainful of UK civil aeronauts, "worshipping at the American shrine", yearning for, in March,1968 winning a US baseline (L.1011).