Over 300 people have got to the summit. Some names that spring to mind are Doug Scott, Dougal Haston, Matt Dickinson and Alison Hargreaves. Not sure if they re all British, though. Hope this helps in your search.
Quite a few. Mallory made his name in the 1920s, Col Hunt was a Brit who led Hillary expedition, and latterly the youngest person to ever climb was 23-year old Edward Grylls who has links with the Isle of Wight.
In these days of guided tours, where less able climbers are almost hauled to the top of Everest, it is hard to keep up. Scott and Haston were the first two that we can prove, in 1975. Rebecca Stephens in - I think - 1992 was the first woman, Steven Venables the first without oxygen and Sir Christian Bonington the oldest. It's easier to answer how many Brits have climed the world's second highest mountain, K2!