I think on certain shows you are allowed to compete more than once -- Fifteen to One was one such example, and Mastermind is another one. Perhaps it was because they were struggling for competitors?
A lot of these contestants have been on other shows.
The other night whilst flicking through the channels I caught the last 5 minutes of an early Bullseye episode and standing there throwing darts for "101 or more with 6 darts" was none other than Daphne Fowler from Eggheads
>>>Come on Jim, spill the beans, which one is you?
A bit of googling (to find out which of those contestants was called Jim or James) has produced a likely candidate but I'll leave it up to Jim to decide whether he wants to tell us his surname.
When these shows were being broadcast I could barely shut up about it on AB (at least in the small corners I was in at the time). Still can't, apparently :/