It's the bit of car ownership that you never see in the glossy magazine adverts. You take delivery of your brand new car and before you've got a few miles down the road you find yourself back at the dealer and trying to get the windscreen wipers to work.

A few days later, water starts pouring in through the driver's door, and the final indignity, it breaks down on the motorway.

They used to be called "Friday afternoon cars" - those produced by workers desperate to get away quickly for the weekend. Even in these days of round-the-clock car production, most factories still seem to churn out the odd lemon.

While it's tempting when you collect a new car to grab the keys and make for the open road, an hour spent diligently examining the bodywork and making sure everything works, is time well spent.

Check the paintwork is regular and unmarked and that the panels are properly aligned - and only sign to take delivery once you are happy.

However, that will only reveal so much. Newspaper motoring sections regularly feature stories of readers who take their car back to the supplying dealer 15 times to no avail - but what should you do if it happens to you?

The Supply of Goods Act 1994 and its update (Sale and Supply of Goods to Consumers Regulations 2002) state that a car has to be "as described, fit for purpose and of satisfactory quality" at the time of delivery.

Clearly, if the car won't drive properly or the doors leak water every time it rains, then you are perfectly in your rights to reject it.

The act actually protects the buyer for up to six years, although, in practical terms, most buyers will want to return the car within six months.

If the buyer returns the car within that period, the burden of proof is on the dealer to show the car was fit for purpose.

Shaheen Musaret, a lawyer who works for the Consumers' Association, suggests unhappy buyers park the vehicle in a safe place then advise the dealer that you are rejecting it, and that it will be returned when the purchase price is refunded.

"This is a huge problem and we currently get 20 calls a day on this issue - and it's very difficult to advise on, as each claim is different.

"Generally, the quicker the claim is made the more chance it has of succeeding.

"We suggest buyers don't let the dealer try and sort out the problem but reject it as soon as they unearth the major fault. Some dealers will do anything to drag out proceedings so that they can argue the buyer is out of time.

"It you are going to let them try and resolve the problem, put it in writing that you reserve the right to reject the car if it fails to remedy the problem."

She says those who buy their cars on hire purchase agreements have an extra level of protection as they can also reject the car to its legal owner - the finance house.

"It will all depend on what's considered reasonable. If you've done several thousand miles the dealer will argue that you've consented to accept the car and can no longer reject it in favour of a full refund."

Even if you've covered a few thousand miles, you are still within your rights to seek compensation if the car is unfit for use - although Ms Musaret suggests you are unlikely to get a full refund.

Lastly, it should be noted that you will not be able to successfully reject the car unless the problems is considered serious.

If you simply no longer like it, or it suffers from one minor problem, you are unlikely get your money back.

Look east for reliability

The Consumers' Association has named the UK's most unreliable car manufacturers and it makes grim reading for those who bought supposedly reliable German marques.

Japanese manufacturers continue to top the table. Honda, Mazda, Lexus and Toyota have been joined by Suzuki for the first time in the "excellent" list.

But the other end of the table German brands are no longer living up to their dependable reputation.

VW dropped into the lowest category last year, and has been joined by BMW and Audi - which has dropped two places in two years.

Ford is the only non-Far Eastern manufacturer to be named as excellent or good.

In alphabetical order, the manufacturers named by Which? as"poor" are:

Audi (1,009)
BMW (1,388)
Chrysler (140)
Citroën (1,243)
Daewoo (266)
Fiat (694)
Land Rover (493)
Peugeot (1,932)
Renault (2,096)
Rover (1,252)
Saab (469)
Vauxhall (2,610)
VW (2,610)

· Source: The Consumers' Association. The survey of 80,000 randomly selected readers of Which? provided information on 34,277 cars up to eight years old. Sample size in brackets.