I was about to say (but you beat me to it) that the serial number bore a slight similarity to Holdsworth(y) and therefore Claud Butler in appearance. But it's not that good a clue to base a definite ID on...still, coupled with the shape of the Path Ends (to be 100% correct, in this case ) I think you can make a case for it being a CB, perhaps a shop-built frame rather than a Holdsworthy factory product (which might explain the low serial number).