Wow, Britain's an even harder country to sum up in four coins. If they were limited to coins form my collection, here's what I'd pick:
Britannia penny, probably one of the earlier types with a ship in the background, like Victoria veiled head. Britannia Rules the Waves, and all that.
Commonwealth "breeches money" shilling - a reminder that English history has it's darker sides.
Queen Victoria "Jubilee" halfcrown. That has to be the apex of British diework.
Gold sovereign with Pistrucci's St George-and-dragon, probably a prewar George V type. Back when the world was on the gold standard, it was British sovereigns the world trusted the most.
Of course, if I was the Queen, I probably wouldn't include the Commonwealth shilling. A nice Elizabeth I milled shilling or sixpence would probably do just as well.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis