You could of course open a NationWide Flexi account and get yourself a bit of plastic. Then in any country in the world that has a hole in the wall machine of the correct type, which is most, draw out cash in the local currency up to Â£200 a time. On your return to the UK you will find no charge for the service and if you did it today in Euro land you would have received â‚¬1.4728 for Â£1GBP which is the official exchange rate at close of business today with no dedutions.
Now you cannot beat that.
You could of course use Saga and lose 3.2 cents per pound, buy more currency then you need or less than you need and have to purchase expensive money in the USA or where ever or lose when you change it back.
travelex.co.uk are identical price today to saga and normally beat all others - you can go into any branch of First Choice Travel and they will match or beat the best deal that you have been quoted (they check it out first)
I bought Â£500 in US $ at Â£1 : $2 two weeks ago from First Choice - no charges for sale or cashback