Oddy

All I do is go to a shop that sells commincations equipment ask for some coaxial cable with braided shielding inside it.
You will have to strip the outer layer of covering off the cable to get to the braided shielding.Then I pull the spark plug cap off your lead slip the shielding over your plug lead solder a wire on to the shielding that is earthed to the head of your engine with a small self tapping screw.Make sure the shielding is isolated except for the earth.Then I cover it with some heat shrink.