I posted a few days ago that I thought my bottom end was on the way out but since the day I posted the knocking has stopped and I have only heard it once since. Could the problem maybe be piston slap? As if it was my bottom end would it not be knocking all the time? So I'm going to drop the oil (Cfs 10/40) classic turbo 2000 running 300+ bhp and change the filter (genuine filter) and see if that solves it. What do you all think?

 

If it was the bottom end it would be there all of the time mate, some of the classics did suffer a bit of piston slap, Have you thought about having a look at the timing belt tensioner they do rattle when there knackered

 

Piston slap will occur when you start the engine from cold. Once it is warm (not just when the water is up to temp) the piston slap noise should clear. Very common problem and nothing really to worry about.