OK, a breakthrough. I pulled out the distributor cap and checked it and the rotor, no mafor problems there and gave it all a quick lick with some emery paper for good measure. I individually tested the HT leads and they all came in within spec. I pulled the spark plugs which were only replaced last weekend and the majority of them were pretty sooty with black matt carbon looking soot. Put it all back together and started it up for the first time after leaving it overnight and straight away it had a horrible idle again. As a last ditch effort i tugged on a few of the leads and found that yanking on number 3 lead i could get a smooth idle, pushing it it would be rough. So it would appear my leads sre stuffed. I have wedged the lead in a spot that keeps a good idle but I do still have the surging idle, could the leads cause this effect also? Would the dodgy leads also cause the sooting up of the plugs even thou it would appear only one lead is knackered? Could the coil be causing this?