As title says... (I have previously used Intersango/Britcoin but don't really trust it atm)
I don't think there is any problem with trust regarding Intersango, but they did have bank issues which means that at the moment deposit or withdrawals are very delayed in GBP (USD/Euro are ok AFAIK).
MtGox is the next option but you need to pay internation wire fees coming in or out, you're limited to 1K GBP withdrawal without getting verified at Gox (which means if you've got a lot then you need to pay the wire fee for each 1K GBP withdrawal).