Re: OP's question. The answer is as per UK Engineering Ltd generally, particularly automotive and nuclear power generation: short termism, incompetence at many levels and politico interference. 1968 Jag XJ6 was long way ahead of the rest of the world, as was AGR, but typical Brit approach of releasing too early and allowing customers to continue R&D to achieve the finished product eventually kills world-beating products.
On a small scale, perhaps only slightly ahead of man-in-a-shed, we can still adminster a sound thrashing to the opposition, eg most F1 teams are based in the UK.
No matter how good the Comet or Concorde were or could have been, if it's built to a price then it has to be built to the cheapest price on a production line. This is something that UK Engineering Ltd has always struggled to achieve against fully resourced opposition.
I could go on ...