Cruising along with one hand on the wheel, he may look detached. But he isn't.

Psychologists say that the average male driver only relaxes like this because he considers his car as a part of himself.

It takes a female driver to understand that her car is a separate entity - which means she is more likely to grip the wheel with both hands.

Research has also found that men use chat about their cars as a way of expressing their own feelings.

Co-author Dr Iain MacRury, of the University of East London, said: "Men talk about their cars as if talking about themselves.

"Women are more comfortable expressing their feelings directly and see the car as separate. That's why women give names to their cars.

"It's also why men drive with one hand on the steering wheel. They are physically relaxed as they think the car is part of them.

"Women drive with two hands because they see the car as more 'detached'."

The study noted where one-handed drivers preferred to put their spare hand.

It found that 46 per cent of men rested it on the gear stick. Just 31 per cent of women did this.

But although only 27 per cent of men put their spare hand in their lap, 39 per cent of women did.

Co-author Dr Peter Marsh said: "Men hate talking about relationships. But the relationship they have with their car is different - because they identify with their cars.

"This is often demonstrated by genuine feelings of annoyance at the threat, or potential threat, of someone scratching or scraping the car. Affectionate patting of the steering wheel, car roof or dashboard, or glancing back as if to say goodbye, are also signs."

The study - called The Secret Life of Cars and What They Reveal About Us - also found that motorists are four times more likely to sing on their way to work than on the way home.

This is because they think of their car as a cocoon - "an extension of their shower or bath". Dr Marsh added: "People wouldn't sing on a bus or a train - but on their way to work in the morning there is a feeling of escapism.

"Most people are gearing up for work at the beginning of the day. It is the last bit of me-time before they arrive at their workplace or desk.

"This mood lends itself to singing, hence the dawn chorus observed during our research."

On their way home, motorists are winding down and are more likely to be thinking about catching up with the news or their families, so sing less.

Cup-holders were said to reveal a lot about a driver. Anyone who obsesses about them is likely to be a workaholic - not wanting to waste a minute.

Dr MacRury added: "Generations ago, luxury cars would have picnic tables installed - now it's a cupholder.

"Cupholders show you live a contemporary executive lifestyle - that your time is precious."

The colour of our cars is also changing. After a decade in which black, silver, blue and grey have dominated, drivers are switching to "expressive" colours such as neon pink, the researchers added.

Their report, commissioned by BMW, is to be used to help plan and design future models.