I happen to be using my hamstrings right now, so if it was my knee I would not let the surgeon fuck one of them up for me. Since it's my hamstring. I would use the allograft, and if this particular surgeon wasn't "comfortable" (he's inexperienced) with it, hire another surgeon. There are others.
Oh, but I now notice you're in the UK. So it's not really your decision to make. So it's not really your knee. Sorry. Good luck.