Is this a question about how to do this in "real world", or from a book-keeping perspective?
In real world scenario, if the company concerned has only a sterling current account, you would have to organise the Euro payment through the bank or via a third party foreign exchange bank such as Western Union.
We buy all our goods in USD, but invoice customers and are paid only in GBP or Euros, so we have GBP and Euro current accounts at Barclays and we use Western Union to do all our USD payments to suppliers.
The process either using current bank or outfit like Western Union is simple, as you basically buy Euros in your case at spot rate for that day/time and send them to your supplier, which the bank/ForEx bank does for you.
Posting on accounts depends if your software package allows multiple currencies etc.
Not sure how much help this will be but I recently had to make a couple of international bank transfers, the first account gave me the option of selecting the currency however this option was not shown from the second account. I would check with the bank first, it may be that payments are only allowed in GBP from that account.
Thanks for the replies. Just as I thought the bank only allows GBP.
The bank the client uses is Card One Banking.
I have never heard of them and personally would have gone with one of the high street banks that supports foreign payments and receipts or opened separate currency accounts.
In that case, just contact Western Union and they would do the Euro payment for your client and you simply transfer them the sterling equivalent (also they are a lot cheaper than main banks for this).