Good question, but if you ask your bank they may know. I think it may be to change it in to euro here, and then the bank can do some sort of telegraphic transfer ( I forget the name of it but I did it to France for only a few euro during the summer ).
Yes WU at the PO seems like the best bet at the moment. Quote I have is €36 for a €500 transfer. Of course I'll have to pay commission on changing the sterling cheque to euros but I guess thats life.