What currency is used?

London uses pounds (GBP). You can get them in a variety of coins and notes:

Coins:

1 pence, 2 pence, 5 pence, 10 pence, 20 pence, 50 pence, 1 pound, 2 pound

Notes:

5 pound, 10 pound, 20 pound, 50 pound

£50 notes are incredibly uncommon so some shops will not accept them/have to inspect them. It is best to avoid paying with these where possible.