Brits are the worst tippers in the world, complaining about having been asked at all, let alone the American custom of 20%!
To be fair in the UK we don't really have much tipping. It's there, but most of the staff in places like restaurants are under full pay anyway. I know in other countries it can differ and can even be up to most if not nearly all their wages are from tips.
But we just don't think about tipping unless the staff really goes out of their way. Otherwise its just service as rendered and thus they get the fee on the bill. Brits are more likely to tip regular places they go to