Gj is correct - this transaction type will be classed as a cash withdrawal and you will be subject to the same higher interest charges applied to ATM withdrawals.
Furthermore, cash withdrawals are treated as low in the hierarchy of payment so if you were to pay only minimum per month or any amount lower than the full balance, you would be paying off your store purchases first, leaving the cash amounts on there earning Tescos more interest.
Not entirely correct - if you buy your euros from Tesco then :
If you pay with your Tesco Credit Card, there's no cash advance fee (excluding Tesco Business Credit Card) or card handling fees. Buying foreign currency with a Tesco Clubcard Credit Card from Tesco Travel Money will count towards a customer's cash limit but will be treated as a purchase transaction and will still be charged interest at the purchase interest rate.