Check your handbook and you'll see it is a 3 year warranty from new with unlimited mileage. The first 2 years are provided by the manufacturer and the third year by the UK dealer network.
I think if you drive a car for 15 miles on a motorway with a warning light telling you the engine is overheating you've got to accept some of the responsibility for the engine packing up and there being a big bill!
My mum once had an engine warning light come on in her BMW, the AA came out and wouldn't let her drive the half a mile to the garage let alone 15 miles! The garage told us that probably made the difference between a £600 repair bill and a pottential £4000 repair bill if she had driven the car any further.
Moral of the story, if you car tells you there's a problem stop and get it checked staright away.