Fan knob off, undo the screw this reveals, prise the radio panel off, pull it out a few inches, disconnect the connector at the rear of the switch, squeeze the lugs and ping the switch out towards you.
Thanks for all the advice, managed to get a switch off a well known auction site £15 including P&P not to bad but still think car spares are over priced. The whole job took about 5 mins but here's a top tip, find a strip of metal (Meccano) and bend it into a "U" shape around the back of the switch to depress the four prongs, makes it a lot simpler than trying to do it with your fingers.
On a general note why are these switches failing ? Mine won't have been used a dozen times in the last 5 years