The Comet tank had first seen service in 1944, fighting in Europe at the end of WWII. During the 1950s, the Comet was phased out and replaced with the newer Centurion tank.
Comets first arrived in Hong Kong in 1949 with the 3rd Royal Tank Regiment. Richard Rinaldi gives their arrival dates as: ‘B’ Squadron ca. May, remainder June".
When Fred Evans arrived in Hong Kong in 1957, the Comets were still here but their days were numbered. Indeed if you look at this timeline of postings for his regiment, the 1st Royal Tank Regiment, you'll see he was part of the "last regular regiment equipped with Comet".
Before he left Hong Kong in 1959, he saw the arrival of the newer Centurion tanks. That marked the end of the Comet's service with the British Army.
Here are some photos of Comet tanks in Hong Kong, mostly from Fred's albums: