[notahacker]

Reaction Engines in the UK spent over 35 years working mostly on that concept (though when they eventually went bust trying to scale up last year I think they were focused on reusable space launch business model which is ironically more realistic)

[ballooney]

No, they were working on the latter (skylon) most of the time, though the new management that came in after their £60M investment quickly dropped SSTO in favour of more immediate RoI applications. The passenger plane was LAPCAT which was a paper study commissioned by the EU. They did some interesting real work too, such as designing and testing a hypersonic engine combustion chamber that could reduce NOx emissions, which would be a big problem in any ‘conventional’ (eg scramjet) hypersonic engine.