It depends upon the retailer. This technology is already available in many other countries and in some it is the expected way to pay for small value transactions. If you see the contactless symbol, you will be able to use your card in this way. If not, you can still use Chip & PIN wherever you see the VISA symbol.
Please be aware that the contactless transaction limit may vary and be more or less than the UK limit, depending on local limits.
You might also be asked for your PIN when attempting to make a contactless payment, this is for additional security.
A fee of 2.75% of the transaction's value is charged for any non-sterling transaction using your debit card. The transaction is converted in to sterling using the Visa Scheme Exchange Rate which can be found on the Visa website