This is a link to the Bank of England's FX database:
http://213.225.136.206/mfsd/iadb/index.asp?first=yes&SectionRequired=I&HideNums=-1&ExtraInfo=true&Travel=NIxRSx
You have to open the "Spot Exchange Rate" link and then select which currency you want as your base currency - either GBP, USD or EUR. Then you can select your exchange currency. For some reason the page flickers back to the top when you tick the box you want, so you have to scroll down to choose which datatype you want - either DAILY, MONTHLY, MONTHLY AVG... etc.
Then scroll back to the top and select the orange "Show Data" link. You can choose your date range and output format.
You can get rates back to 1963 for most currencies.