What I posted was the recommendations of the AA.
I had an XJ6 jag which was in the garage for service and an apprentice used it to jump another car off. The end result being it "fried" my engine management card. The garage replaced this at great cost. This prompted me to read the "manual" and Jaguar had a paragraph warning against used the "negative" terminal on the battery, but to attach the lead to the engine "body" I think they would know.
