As a ex B.E.A. avionics man there were many reasons why the Vanguard failed . 1/ those 14ft 6ins props produced a great deal of interior noise and vibration ,we spent £1000s of pounds trying to cure this problem to acceptable levels and didn't cure it properly. 2/only the five 951s ever had Club seats and as the planes popularity waned they were converted to Tourist class 3/ they were very labour intensive the electrical system was over complicated as the tail de-icing was electric mats, the built in air stairs were heavy and fragile .we were glad when they were withdrawn and 9 were converted to freighters they made great freighters could carry 19metric tons of freight were fast and carried on flying until 1996 [freight and livestock don't complain] still love working to preserve the last remaining one at The Brooklands Museum though I would never have said that in the 60s and 70s.