I have a hermanns tortoise and I have noticed that his back lags look very dry and there is a thin bit of skin that looks like it is just under the shell near his back legs and the ends of it are hanging off, I was wondering whether anyone knows why this would happen or if I should just take him to the vets?

Yeah thats fine, sounds like he's shredding -unlike other reptiles Torts don't shred all their skin at once. As long as it's not sore (pink or bleeding) then leave alone, you can bath if you want but don't pull the skin off, it will come of naturally

Thanks for the reply, I'm just worried about the long thin piece of skin that is hanging off just under the back of his shell, is that normal?

I'm sure thats all it is, if you're worried see if you can get a photo, if you can't upload it on here but have a camera phone, pm me and I'll give you my mobile no and you can send me a picture via text/mms. Whats the skin like underneath it?

Dawn is correct, tortoise shedding its skin.
Whatever you do dont be tempted to pull the skin off, it will come off in its own time. You dont want to pull it and make a sore area, where bacteria can set in:0)