Kevin
Haven't complete yet, but my solicitors have offered to organise the bank draft for us.. so we're transferring all of the funds (final stage payment + their fees) to the Sols in advance and they'll make the payment at the Notaries... with no additional charge.
I've read that others have been told that their Spanish Banks were going to charge quite a bit (between 50 and 100 euros) for a bank draft, which sounds scandalous to me..
Your other option is to organise the transfer direct to PW but you have to do that in ADVANCE of the completion date. Doesn't sit right with me (moving ££ without having snagged or signed the paperwork first), but if you wanted to go down that route you could use any of the Exchange organisations - e.g. HiFX, Moneycorp, TORFX and many others. Shop around to get the best rate, and also get confirmation if there are any carges for the transfer (some do, some don't - so be wary).
HTHs
Russ