The UK Government that signed the 1962 agreement with France, was a Conservative one.
Labour ones twice came close to cancelling it, then another Tory government, under one Maggie Thatcher, was quite happy to finish Concorde, but BA
accepted their not very serious offer to take over support, in exchange for keeping all profits (previously-the Government took 80% of any profits).
Whilst an EIS on the early 70's was desireable, it was just never going to happen.
Apart from anything else, the Comet 1 experience had led to a very conservative, cautious approach, some older people at the time also cited the R-101 airship experience too.
My senario above was based on Concorde B and nothing else.
Without a '73 oil crisis, it might well have been different, several dozen aircraft maybe.
Also, it's worth remembering why PA cancelled options in early '73, which had a massive effect on the attitudes of other airlines.
Though they had real Concerns that making a PA Concorde profitable would be a given, PA were also in financial trouble anyway, partly through over-ordering 747's (which they'd repeat again a few years later with the 747SP).
Perhaps another factor too.
PA had actually, before BOAC or AF
, been the first to take out options in 1963.
Juan Trippe, PA's influencial CEO, had another motive beyond putting PA in the forefront of SSTs.
He wanted a US SST programme.
The options did the trick, soon after JFK
announced the effort, Boeing would in 1966 get the contract, a poison chalice given the wildly over ambitious FAA spec, again a result of JFK
, who wanted bigger (fair enough) but also faster, big mistake.
You cannot help thinking that something like the 2707 was what PA always had in mind, Concorde would be the entry level SST, a Comet 4 to the DC-8/707 in SST terms.
So when 2707 was axed in 1971, perhaps PA were from then always looking for a way out, 2707 going would also put a question mark over Concorde, would it be allowed to land in the US-Some in the Nixon administration said 'no' at the time.