I don't know if this is a "British" thing or not. I tend to think "not."
I think the recent downturn in the economy has a led a lot of people to behave somewhat differently than they did before. I think you would see some of the same behavior on mostly American ships, too.
But the Brits also have a unique "problem" in that Brits are not used to being required to tip for service. Many cruise lines imposed mandatory service charges because many Brits did not tip and I am guessing some Brits now feel like "well, obviously I am now forced to pay for the service, so I am going to get my money's worth."
While service used to be viewed as more of a courtesy in the eyes of Brits, now on cruise ships it has become a commodity - something that they pre-paid for and now expect to see a return on their investment.
What do you think of that theory?