Finally after 2 days I've managed to change my water pump, idler and tensioner rollers and cambelt (spent most of the time driving to Halfords/motor factors for tools).
I tensioned the cambelt using the KM-666 tool. Popped the tool onto the tensioner pulley and the backplate. Rotated the crank 7 teeth on the exhaust sprocket and then did up the tensioner bolt. I tested it by hand and couldn't get the belt to turn quite 90degrees between the idler roller and exhaust sprocket.
Having now driven the car, I noticed when I pulled up and left the engine running a "belt" noise (how else can I describe it?) and I'm wondering if I could have over-tightened the belt using the method above? It may be my alternator belt which I did do quite tight but I've not checked yet.
Any advice welcome.