This is a pretty unusual board made by Steve Inglis and Wes Clarke for Inner Visions surfboards in around 1981. Its got three big fin boxes which could allow all sorts of fin placement; its unusual for the two forward boxes to be so large and they're actually shaped into the rail channels. The channels are unusual as well for a UK board, most were belly channels and a couple of years later. I've seen rail channels on late 70s Aussie boards, they must have been a bugger to shape. Its 6'3 x around 21 1/2.
Inner Visions were one of the main late 70s board makers in far west Cornwall, based in Penzance and St Ives. But having said that you don't see many around today. Mabye board making only lasted a few years and their surf shops lasted longer.