If you get the following error when trying to checkout it means that in the past you have either:
Bought a UK O2 plan and are now attempting to buy a Europe plan
Bought a Europe plan and are now attempting to buy a UK O2 plan
The problem lies in the fact that each email address can only be associated with 1 currency – either GBP or EUR. The only way around this is to use a DIFFERENT EMAIL ADDRESS to make the second purchase.
Sorry, there is a problem
We are sorry but our records show that you have previously purchased a plan from us which was priced in the currency GBP. Unfortunately we are unable to add another currency to your account, in this case EUR. If you need to purchase this plan then you will have to register using a different email address. We hope that you do and apologise for the inconvenience.