The currency in Sousse is the Tunisian dinar.
Take pounds with you to exchange when you get there, as you can't take dinar in or out of Tunisia. There are banks, post offices, bureaux de change and ATMs where you can swap your sterling for dinar – keep your receipt so you can change it back again at the end of your holiday. You can also use your debit or credit card.
And when you're planning your next holiday, take advantage of the excellent rates at Thomas Cook Travel Money and remember to pop your travel money card in your wallet before you go.