The official currency in the UK is the British Pound Sterling (GBP), and is decimal based like the dollar, there are 100 pence in a pound. The coins are 1p, 2p, 5p, 10p, 20p, 50p, £1, £2. The notes start at £5, £10, £20, and £50 pounds. You won’t often see the larger notes any more to combat loss to counterfeits. There are other currencies as well, though I’m under the understanding that in Scotland, some of the Channel Islands and elsewhere, they have their own printed/minted coins and notes, they are exchanged at the equivalent of the Pound Sterling. Scottish notes are legal tender in the rest of the UK, but Channel Islands notes and coins are not.
The Euro is a topic of great debate. In short, it is a “new” currency that has begun in recent years in the European Union. Britain however has not gone in as of yet. They are waiting to see how it goes in the other countries before they join, and there is a strong public opposition to doing so. There are very few shops that are taking the Euro so it is not advisable to use Euros if visiting, you also will get a lousy exchange rate in the shops that do.
There is more about the Euro here, The Euro Debate.