It is often not the value of the handheld device which is important but the content

Magnus Ahlberg Pointsec

Drivers found an average of three phones per taxi in that period, according to the survey by the Taxi Newspaper and security experts Pointsec Mobile Technologies.

And passengers are often not fussed about recovering their mobiles with only half of the phones reclaimed.

A different story applied to portable computers and PDAs, with owners coming back for 93% of laptops and 85% of PDAs.

Diamond stash

Taxi drivers have also found bizarre items left behind including a little girl, a basket with a cat in it and a goldfish in a water-filled bag.

On the plus side, one discovered a suitcase full of diamonds while another found �2,000 in cash - although both were returned to their rightful owners.

Stuart Pessok, editor of Taxi Newspaper, warned commuters to take care when on the move.

Businesses now risk losing valuable or confidential information stored on handheld devices through the carelessness of their employees.

Content value

Tabloids have previously seized on the secret agents and civil servants who have compromised confidential information by leaving laptops in taxis.

Magnus Ahlberg, managing director of Pointsec Mobile Technologies, added: "It is often not the value of the hand-held device which is important but the content.

"If lost or stolen this can put a company at serious risk of sabotage, exploitation or damage to their professional integrity."

A total of 131 of London's 24,000 licensed taxi drivers were questioned for the survey.