Ok, so further to this thread, I thought, why not pay a bit less for the car and use the saved money to buy a warranty.
Because for a warranty to be actually worth having the car needs to be under 7 or so years old and under about 80k miles. Otherwise the exclusions and customer contributions begin to make the whole excercise pointless.
And this is across your life of ownership - so you need to buy at about 5 years old and 60-70k miles in order to get 2-3 years of no hassle warrantied ownership from the car.
A 5 year old 70k S Class is not £6k.