In an ongoing battle between the candidates to appear more down-to-earth, the Democrat's campaign branded the Republican as out of touch and guilty of betraying US workers, after it was reported that Mr McCain and his wife Cindy's vehicle collection included a Toyota, Honda and a Volkswagen.

Mrs McCain's principle car, according to investigations of public records by Newsweek, is a Lexus with the private number plate "Ms Bud", which is registered to the Budweiser beer distributorship and fortune she inherited from her father.

Mr McCain said in a recent interview with a television station in Detroit, the heart of the struggling US car industry that "I've bought American literally all my life and I'm proud".

But the United Auto Workers union (UAW), which has endorsed Mr Obama, accused the Arizona senator of deceit.

"When he's in the Midwest, he tells voters he supports the industry," UAW president Ron Gettelfinger said, referring to economically bereft battleground states.

"That's a really a nice campaign line, but it turns out that John McCain wasn't being straight with the people of Detroit," he added.

By contrast, Mr Obama and his wife Michelle own a single car: an environmentally friendly 2008 Ford Escape hybrid. It was purchased last year to replace the family's Chrysler, a "gas-guzzler" which was ditched after complaints that Mr Obama was lecturing Detroit on building more fuel-efficient cars.

It is the second time that Mr McCain's wealth, which is almost entirely derived from his wife, has become a campaign issue. In July he revealed that he did not know how many properties the couple owned. The answer was seven.

After Mr Obama made a remark about rural voters clinging to guns and religion in bad times, Mr McCain's campaign and his supporters have tried to portray the Democrat as an aloof liberal unfamiliar with ordinary people's priorities.

John and Cindy McCain's cars:

Cadillac CTS made by General Motors (US)

Volkswagen convertible (Germany)

Honda sedan (Japan)

Half-ton Ford pickup truck (US)

Willys Jeep (US)

Jeep Wrangler (US)

Lincoln (US)

GMC SUV (US)

Three NEV Gem electric vehicles - bubble-shaped cars popular in retirement communities (US)

Lexus - registered to Cindy McCain's family's beer business with MS BUD number plate (Japan)

Toyota Prius bought for daughter Meghan (Japan)