Just use
www.transferwise.com. Simple, easy, great GBP to USD/EUR rate, low fees. Next day SEPA transfer to MTGOX (if you are verified with MTGOX).
Yes, TransferWise does seem rather good for sending money to the EU/US.
I guess they can't really help with selling Bitcoins for GBP though? Or can you withdraw from MTGOX to Transferwise who then send it to the UK somehow?
Besides, it does still seem like we should have a UK exchange - we don't have to wire money to the US to buy things from Amazon, do we? Why should we have to for bitcoins?