An outbreak of male paranoia is guaranteed today with the finding that one in 25 fathers may be unknowingly raising a child who is not his own.
A review of studies of DNA profiling, the ultimate proof of a genetic relationship, shows that the rate of "paternal discrepancy" - where the man tested is not the actual biological father of the child - ranges from 1 per cent to 30 per cent.
Researchers from the Centre for Public Health at Liverpool John Moores University say the average rate is 3.7 per cent, equivalent to almost one in 25 who discover they are not the true fathers of the children they call their own.
The revelation can be devastating for families but the implications have not been understood, say the authors of the study, in the Journal of Epidemiology and Community Health. In the UK, about a third of pregnancies are unplanned and one in five women in long-term relationships has had an affair.
The total number of families affected will be much higher than one in 25, the researchers say, because for every "false" father identified through testing there will be a true biological father elsewhere, possibly with a family of his own.
The use of DNA testing is increasing rapidly and the judicial and health systems are reliant on it for procedures such as organ donation and criminal identification. In some cases, such as identifying disaster victims, DNA tests have unwittingly revealed some with a different biological identity from the one suggested by their credit cards, clothes and personal possessions, adding to the distress of surviving relatives.
Professor Mark Bellis, chief author of the study, said: "We know infidelity breaks up families. Twenty per cent of divorces feature claims of infidelity by one or both partners. There are issues about the mental health of the father, or the person who thought he was the father, as well as the woman and the child.
"More and more people are taking these tests and they may receive some of the most fundamental information about themselves and their closest relatives for which they are unprepared. We have not looked at the consequences of giving this information, or withholding it."
The impact of paternity testing was brought home during the public break-up of the relationship between the former home secretary David Blunkett and his former lover Kimberly Quinn after he demanded access to the child whom testing proved he had fathered.
Several soap operas, including the now defunct Liverpool series Brookside, have featured plotlines about disputed paternity and the Human Genetics Commission has expressed concern after the results of paternity tests were broadcast live on ITV's Trisha show.
DNA testing can be done using a hair follicle or mouth scrapings, and is available by post from commercial agencies. Some countries are considering outlawing the genetic testing of children without the consent of both partners.
'I knew he wasn't my son'
Ian Gould proved he was not the father of his estranged lover's son - after 13 years of paying maintenance. He was named in a paternity claim in the 1980s before DNA tests were available, and had the same blood group as the child, which gave him a 35 per cent chance of being the father.
After paying out £8,000 for the son he had no contact with, the CSA demanded in 1994 that he increase weekly payments from £12 to £85. He refused, insisting he was not the father. A DNA test proved they were not related. The CSA refunded cash paid since 1994 but not payments made before then.
Mr Gould said: "I knew in my heart that Craig wasn't my son. It has been heart-rending at times. When he was 11 he came to our door and said he wanted to get to know me. His mum had drummed it into him that we were father and son."
He added: "The CSA just wouldn't listen."Reuse content