There's a scene in the first episode of Sherlock where it's pointed out that Dr. Watson is a "British doctor injured in the war in Afghanistan" - I laughed. Apparently I was the only one in my circle of friends who got that that was the original character's biography, written in 1887!

Right, but that's happening _now_ so we (well, the people who are doing it) have the power to prevent it.

These are individual people. If the British government was to complain, then that could be considered hypocritical. But an individual person can't be held to account for actions taken, by others and (quite probably) before they were born.

What if they are still benefiting from those historical acts ?

Name a country where you can live without unknowingly benefiting from some atrocity in the past.

Not the point. Whoever you are, if you have ill-gotten gains (more than average at least), even as a gift, you have a moral obligation to use them to counter the ill.