I don't really tip anything, it isn't part of UK culture.
If at a restaurant and the bill is say £48, then I would leave £50 if paying in cash, but virtually everyone pays by credit card here so you always just pay the exact amount.
It's not because we are tight, just different, we probably pay a lot more than you for everything. My hair costs £80 ($132) to have cut/coloured (that a pretty average price, there are far more expensive salons, and I don't even live in an expensive place in the UK, London you could pay 3 times that), why would I tip on top of that, I think it's enough, if they do a good job - great that's what I have paid them for anyway. I wouldn't expect them to do a bad job for that money.
Same for restaurants, it normally costs about £50-60 ($82-100) for 2 people here for a decent place (again, you can pay anything up to 10x that), again, I expect good food and service for that anyway.