Given the fees involved, I've found it best to transfer money as infrequently as possible, making large transfers (at least £5,000 or 10,000) each time. The problem seems to be that, with a wire transfer, there is normally a charge at both ends of the transaction - from the UK bank making the transfer and another from your French bank to "receive" the money. You could probably manage on two to four transfers per year.

Besides, you'll need some money in your account in the UK for when you are back in the country.
Cheers,
Bev