It was the Convair 990 Coronado although the Trident was not far behind.
The Comet was only a .72/.75 airplane.
The VC10 would probably be capable of Mach 1 and one was rolled when the F/O got it wrong on a Dutch Roll exercise. Although to watch the horizontal though the periscope while that was happening would be rather exciting.
BOAC also had a 707-436 that they lost control of in the same exercise and that was recovered over the sea off the SW UK coast at a very low altitude. It is believed to have gone supersonic as they pulled over the top on recovery.
But the fastest was indeed the Coronado and they have all gone now after Spantax got rid of them.