Lois Rogers, Medical Correspondent
 

Some laboratories have reported the level of "unexpected" paternity to be as high as one in seven when they perform DNA genetic tests on blood samples from supposed parent and offspring.

There are now seven government-approved laboratories doing paternity testing. Cellmark Diagnostics in Abingdon is the largest and receives more than 10,000 requests a year. One in five of them is "private" and has not been ordered as a result of a court or Child Support Agency dispute.

David Hartshorne, spokesman for Cellmark, said that in about one case in seven, the presumed father turns out to be the wrong man.

"It is surprising how often the mother is wrong about the person she thinks is the father," he said. Marriage breakdown and more births outside marriage have increased disputes about paternity and the desire for testing, he added.

In addition to DNA evidence, other studies of mass blood samples suggest that increasing numbers of women are unsure if their husbands are the fathers of their children.

This phenomenon of misattributed fatherhood has been investigated in a newly published study by social scientists at the London School of Economics (LSE).

Oliver Curry, the principal researcher, said long working hours and commuting by fathers could contribute to uncertainty about whether children have been fathered by the man who is bringing them up.

"It can have major consequences for the way men treat their supposed children and the amount of time, money and emotion they invest in them," Curry said. "It can range through the entire spectrum from serious abuse to deciding not to pay for their education, or not buying them the latest expensive trainers."

The team from the LSE is calling for investigations to be set up by the government's new National Family and Parenting Institute. They believe that mistrust over paternity may be an overlooked factor in family breakdown. Women are driven by primitive urges to seek the optimum genes for their children, which can lead to them sleeping with a "high social-status Casanova" as well as their regular partner during the fertile period around ovulation, researchers claim.

David Buss, a psychologist from the University of Texas who is about to publish a new study on the subject, said: "A proportion of these misattributed fathers will believe that the child is genuinely theirs, and often the mother tries to foster that belief."

He also estimates that the tendency for women to shop around for the best genes leads to them making mistakes about who has fathered their child.

Soraya Khashoggi, 57, former wife of arms dealer Adnan Khashoggi, has revealed how DNA tests established her 18-year-old daughter, Petrina, to be the child of Jonathan Aitken, the disgraced former Conservative minister.

Khashoggi said her ex-husband had completely accepted Petrina: "He gave her his name without ever asking who her true father was," she said.

Paula Yates, the television personality, discovered at 37 that her real father was Hughie Green, the Opportunity Knocks star.