There is a simple answer to this. When travelling, take out cash from local ATM machines using either your own UK ATM card (if it has a cirrus, maestro, plus, or similar symbol on the back). Use your UK credit cards as a backup option (because they will be slightly more expensive). For other purchases, use your UK credit cards. Small charges apply, but they are nothing compared with forex companies, including the major banks.
NEVER EVER use any UK forex companies, or banks for that matter. The spread of buying vs selling rates in the UK is one of the worst in the world. Any discussion of one institution over another is "rearranging the deckchairs on the titanic".
I usually take a small amount of UK sterling cash with me, which can be exchanged locally in emergencies.
You typical savings from doing this are considerable. The way to look at this is to check the percentage spread (difference between buying and selling for the same currency on the exchange board in a forex dealer's office), then add the percentage difference between their exchange rate for a given currency and the bank selling rate (NOT the rate they show in branches, but the rate they show on websites for substantial transactions). This will show the total amount they are scamming off you. It is possible to save 10 - 15% by doing this. Given typical spending on a holiday abroad, I would guess several bottles at duty free!