How long is a "lifetime?" For Vauxhall, it's 100,000 miles. And for anyone buying a new Vauxhall, the company is trumpeting its new "lifetime" warranty.

But, in addition to the mileage condition, which for a driver covering 400 miles per week is only five years, there's a more insidious part to the small print.

For the warranty is available only to the first owner.

So, those who purchase a pre-registered car (a trick used by manufacturers to boost their sales figures by having dealers formally purchase cars at a discount, then selling the cars as technically used even though they may have been driven for only a dozen miles or so) the warranty does not apply. Nor does it apply to anyone who buys a car from a leasing company at the end of an agreement even though many leased vehicles have very low use.

And, of course, it does not cover any second or subsequent buyer who purchases a car from a dealer who has taken it in part exchange or from a private seller.

It's a great marketing gimmick but of no use in the second hand car market.

That, of itself, does not matter to Vauxhall - but it does matter to their dealers who, in a few months time, are going to have to start telling customers interested in a trade in that the advertised benefits are not available to them. And annoyed customers might just go somewhere else.

The adverts contain details of the limitations - but only if one reads the (literally) small print at the bottom.

UK manufacturers are having to look for ways to draw in the customers: second hand cars are a remarkable bargain in the UK at present and now all financial-crisis incentives have expired, the industry is on its own. First signs are that it's not doing too well.

The Society of Motor Traders and Manufacturers last week said that official figures show that July's sales numbers showed a dramatic turnaround - in the wrong direction. For the first time in more than a year, new car sales fell. And they did not fall by a little: they fell by 13%.