OK, at the risk of making myself look a complete tw*t, here's a tip some of you may find useful. This is my 1st 8v gti, came to change plugs / leads etc having done my own servicing many times before, put some bosch super 4's in with new bosch leads - thought to myself, these leads don't seem to fit right on the plugs, and I got an occasional missfire - must have bought the wrong leads. No - apparently you take the screw-on end piece off the plugs - and hey presto - perfect snug fit. Doh! Idiot!