Hello Sir,
Its can be done any how.
Are you talking about registered user or unregistered users? How you wanna to detect a user, price will work GBP for him and Euro for her? It can be some ways:
01. When a user will register, then the currency can be select by user or it can be select automatically by tracking his country and area.
02. For unregistered users, you can tract their IP and can then select the currency for him.
03. For unregistered user, when they will go to they shopping page >> Payment Page >> Will select Currency by him.
If you any idea you can share. I am confident can be done everything, love to take new challenge things.
I look forward to your response.
Regards,
Shumon Iqbal