This is an authorisation charge and is immediately reversed. Depending on the bank, it will be removed from your statement in anywhere from a few minutes to a few weeks.

When you enter your payment data, our system sends a request to your issuing bank for either a £0 or a £1 authorisation to verify that the card is issued and the bank will allow it to be authorised, the authorization charge is immediately reversed. However, even if the bank declines the transaction, some people may still see an authorisation for £1 on their credit card statement. The important thing to remember is that this is not a charge, and it will disappear from your statement; depending on the bank, it will be removed from your statement in anywhere from a few minutes to a few weeks.