What I didn't tell you about was the conversation I had with the mechanic. The tow truck had been sent out to me - twice. The first time, the car was 'fixed' by the roadside. The repair lasted all of 20 miles, and then I broke down again. This time, a roadside repair wasn't possible, and I had to be towed to a garage.
The mechanic spent about an hour with his head under the bonnet. When he came back out to me, I nervously said, "So, what would you say is the best thing to do?"
He scratched his head, thought for a bit, and then said slowly, "Well, what I suggest is that you take off the petrol cap .......... and then screw a new car in underneath."