The Advertising Standards Authority described as "misleading" adverts by leading companies outlining a scheme where customers pay a monthly fee of less than �200 for a new car.

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Upholding three complaints against Ford, Mercedes Benz and MG Sports Cars, it said the advertisers had failed to give enough emphasis to other charges.

It said the car makers did not make clear that customers must also pay a deposit of up to 25%, and a final payment of up to �12,000, before actually owning the car.

The ruling comes weeks after the Competition Commission accused the UK car industry of "fixing" prices.

An inquiry was launched by the commission after concerns that the cost of new cars in the UK is higher than for the same models elsewhere in Europe.

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The ASA noted that all three companies had included details of the extra charges, usually in a footnote at the bottom of the page.

Each manufacturer argued it had made the charges clear.

But the watchdog ruled that by emphasising low monthly payments without doing the same for other payments, one advertisement "misleadingly implied readers could by an A-class Mercedes-Benz for �183 each month".

A Mercedes-Benz spokeswoman said: "We never meant to mislead anyone and our advertisers checked the ad with trading standards officers.

"As far as the ruling goes we take it seriously and take it on board."

The complaints were made after a member of the public approached East Ayrshire Council's trading standards officers.

An ASA spokesman said: "What can look like an extremely attractive deal can actually be much more expensive. There needs to be much more transparency and clarity."

But MG said similar promotions were used throughout the car industry and most consumers would understand the implications of such schemes.

A fourth complaint against a similar regional advert for the Land Rover Freelander by a Scottish dealership, was also upheld by the ASA.