Found the official GoPro Suction Mount on Tweeks Cycles website for £24.98. Free standard delivery included.
Cheapest I've found. Amazon currently selling for £39.95, Argos £39.99, Currys £39.99 and GoPro website £39.99. Making this £14.98 cheaper than Amazon.
Attach your GoPro to cars, boats, motorcycles and more. This industrial-strength Suction Cup mount is proven at speeds of 150+ mph and engineered for stability and a broad range of motion. Adjustable arms allow for ultra compact mounting. Includes a standard base and a quick release base for moving conveniently between shots and locations. For maximum holding strength, attach to a clean surface.