Note to myself - must visit pprune more frequently. What an interesting topic.
I have always had the opinion that the British aircraft manufacturers were there own worst enemies when it came to commercial promotion of their own designs.
Since the inception of aircraft building in the UK, manufacturers had, by and large, built aircraft to government contracts, whether military or civilian. Look at all the airliners built in Britain in the 1920s and 1930s. Virtually all of them were made to suit Imperial Airways requirements with no thought given to sales to other "foreign" airlines (with the noteable exception of De Havilland). That trend continued into the 1940s and 1950s. Was not the Brabazon Committee just another example of this methodology? Now and then, one of the designs would find a niche for itself in the world market but, most of the time, the designs either flew in prototype form only or were tailored so close to the state airline's requirements that they were unsellable elsewhere - even to other British airlines. Often the state airlines' requirements had changed by the time the plane was ready to enter service so ended up being ordered in miniscule numbers.
The manufacturers found it very hard to break away from this commercial "model" and when, in the 1960s, the need to compete on a world-wide commercial basis became apparent, they found themselves lacking. It took quite a few years for a more marketing based commercial approach to sink in and by then the number of manufacturers had severly reduced.
Old habits died hard. Even in the 1970s Hawker Siddeley were reluctant to go ahead with the HS146 without government backing. They had to wait until BAe was "nationalised" in 1977 beffore the project was resurrected. I wonder how successful the plane would have been if it had gone ahead in 1973 rather than 1978?