I seem to encounter this problem a lot as well. I don't think I fly overly tight circuits (unless I know I'm the only one using the field then I like to have some fun), but I do keep them reasonable and I seem to be forever running into people who love to take the really scenic route. It's even worse when it's a microlight doing <70kts.
I have become quite used to asking politely if I may overtake on the inside. I remember having to do this a couple of times as a student as well, although was more reluctant to then. I personally have never had anyone give me any bother about the request and they are normally happy to coordinate (non ATC field I should mention of course).
I did have it one time going into Biggin Hill when there was a twin (I was in a twin as well) doing massive circuits. After 2 requests from ATC to keep it inside the ATZ, he was asked to orbit at the end of his downwind leg and report ready to rejoin.