Ground post for when requiring a jump start

I recently had a situation whereby if I wasn't at home at the time my battery went flat I would have needed a jump start.  Reading the Jaguar handbook, and also by searching the internet I came across an important instruction.  It says to connect the donor vehicle "positive" jump lead to the battery positive and with the other end of the jump lead, to the disabled vehicle battery positive pole.  That I have always done correct.  It then states to connect the donor vehicle "negative" jump lead to the recommended "ground pole" on the donor vehicle (not the battery!) and the other end of the negative jump lead to a suitable earth point on the disabled vehicle at least 20" away from the battery! 

I have to confess that in all my years of motoring, on the odd occasion that I have needed jump leads, I have connected the ground to the battery "negative" pole.  I know the implications are that there is less resistance when you connect to a good solid and clean part of steel rather than earthing via a relatively small diameter jump cable which is going to get very hot! 

What I don't know however, is exactly where this earth pole is on my XF!  

Regards

Graham