Oh Andy you are having no luck at all with this car mate, I will have to hear the knock to have any idea of what it could be sorry, if you rev the car lightly from the throttle body (where the throttle cable goes to) does the knock go away? also if you give the engine a rev then rev it again as the revs are dropping of (if that makes sence to you) does it knock at the point you catch it as the revs are dropping off?
I am hopiing its just piston slap, fingers crossed.
Cheers Iain