I recommend curencyfair.com – set up an account, transfer pounds from your bank to theirs, exchange the pounds to CHF (peer to peer + very small %) then transfer them to the swiss account (£3 fee). Because it’s peer to peer you’re getting a rate midway between the usual buy and sell price – the commission is something like 0.3%. I usually save about £50 plus the bank fees on renting a ski apartment.
No connection with them other than as a satisfied customer – I get nothing out of recommending them other than the satisfaction of helping other avoid excessive charges for what is now a very simple transaction.