It's terrible when it happens; I know, it happened to me about 3 years ago. I was punched on my driveway and the keys grabbed out of my hand. The strange thing was it was stolen from Wythenshawe by some local scallies, but turned up a couple of weeks later in Frodsham! The police think it may have been stashed there in case it had a tracker fitted.
It had false plates on it (which would have been from a Mk 1 not a Mk 2 given the reg no.). It had an extra 500-odd miles on the clock, which means it would have been filled up at some point, so the tea-leaves must have either paid for their petrol or driven away. If the latter, surely the police could have checked up.
And Chester's supposed to be so posh, as well!