When someone extols the virtues of the third party car insurance they have on any other car they drive, remember that it's third party... ie, it'll only pay for any damage caused by your car to others.
And if you've never been in a car with them driving, think loooong and hard about whether or not it's worth it when they say it'll be quicker to drop you off at the tube station and they'll drive your car for the day...
More on this once the legal team have cleared the copy...