My 12month old labrador-dalmation is a very itchy boy at the moment. I put on a flea treatment about 3 weeks ago and also gave him a quick shampoo (as he smelt rotten after being in kennels for a week whilst we were away.) And although I can't see anything wrong with his coat (he's very glossy), he's always scartching - particularly around his snout and mouth.
I've recently changed his diet to raw meat/bones etc... could this be the reason or is it something more sinister?

It could be the fact that you've changed his diet and beef or what ever meat your feeding isn't agreeing with him, try to think back to when he first started doing it and go from there.  Just make sure he hasn't got any bones stuck around his teeth because dogs scratch their mouth if anything gets stuck in there.

Warm regards Susan