Just an update on this, I am going to change the engine. Air seems to be getting past piston 1.
I have been advised the pulley fitted to my car is not correct, and at some point in its life it may have had a cambelt snap and then repaired badly, although the pulley could have come from Renault, it seems very unlikely as the belt is over 5mm from the edge.
Instead of digging into the engine, with the cost of 3 hours labour plus a new pulley before I even know what is actually the cause, I am going to change the engine as it seems easier in the long run... The cams I was going to have will be put into the new engine and all should be up and running in about 2 months time I hope.