Well I did go ahead and buy a Crank Shaft Sensor and a Cam Shaft Sensor, in total that was about £50...
...but on the plus side I do now have two very lightly used sensors that I could sell.
Besides that it's just cost my patience and sanity for a few months!
Unfortunately where I am at the moment I don't have any access to decent tools so I'm yet to strip it down and fix it properly... I'm expecting to be able to fix it when I've got it in bits but worst case scenario I'll either disable it's operation (it's much more a convenience thing that anything mechanically important) or replace the valve unit.