A man whose Porsche was stolen when he left the keys in the ignition while he went to pay for petrol has been found liable for the theft by the Court of Appeal.

The ruling has weighty repercussions for the wording of policy documents, and is heralded as a victory for plain English contracts.

Richard Hayward, of Cwmbran in South Wales, had successfully sued Norwich Union (NU) in 1999 to force it to pay out on his £76,000 claim for theft because the policy wording was not clear.

The High Court held that the words “left in the car” was ambiguous and had to be interpreted in the insured's favour as meaning “left unattended in the car”.

Hayward argued that the immobiliser fitted in his car was the principle defence against theft.

The thief had a scanning device which could override the immobiliser.

The judge went on to find that the car had not been left unattended because Hayward was close enough to it. He ordered NU to pay the claim.

But the Court of Appeal overturned the ruling this week, saying Hayward was too far away from the car.

Moreover, Justice Peter Gibson ruled that a sentence in a policy which is written in ordinary English and which has been drafted in a user-friendly, untechnical way should be construed unambiguously.