Welcome to HT Mike

You can exchange English Sterling (not Scottish, Welsh or Irish) very easily, try and make sure that your £ notes are in a good condition.
There is an exchange within the airport that you can use, and your hotel will also be able to exchange money for you, there are also plent of ATM's around. The exchange rate is fixed so you will get the same rate everywhere.

There is more info in this topic http://www.holidaytruths.co.uk/viewtopic.php?f=27&t=144249

If you enter Hammamet in to the search facility at the top of the page you will find a lot of topics with information.

Anything else just ask
Graham

Brilliant thank you very much Graham,I can't wait to go :-)