Thousands of men are turning to DIY testing kits - available online - to discover whether they are the biological father while they are still in a relationship and without telling their partners about their suspicions. Some have brought up children to adulthood or paid tens of thousands of dollars in maintenance to the Child Support Agency (CSA) before finding out they have no genetic link.

Men's Rights Agency co-director Sue Price said: "People's lives are being ruined by this. It is not just the men, it's the children who grow up thinking one person is their father and then find out it's someone else. "In the future, more and more health treatments are going to be based on genetic technology, so it is going to be even more important to know who your biological father is. "Mandatory testing would get rid of all these problems."

The DNA Bio Services lab conducts more than 2000 such tests a year from the sale of its DIY kits. New 2007 figures compiled by the company show that one in 4.5 paternity tests exclude the man as the biological father - a record high since DNA testing began 10 years ago. Managing director Gary Miller said: "The increase is across all social classes and ages - it affects everyone.

"Before, a lot of the work was for men who had been contacted by a woman or the CSA for maintenance and wanted a test to prove they weren't the father. "Now we see a lot of men in a relationship or just out of one who are just looking for reassurance that they are the father and then find out they're not and are completely devastated." Under Australian law, the family courts will only order a paternity test if there are reasonable grounds to doubt that the estranged partner is not the biological father.

The CSA does not require proof of paternity beyond a birth certificate or acceptance by a man that he is the father. This means some men pay tens of thousands of dollars through the CSA before finding out they are not the father. Even if they have brought the children up for years as their own, they are then denied any legal rights of access to them.

Some experts say the proportion of negative paternity tests reflects the fact that the men coming forward already have reasonable doubts, and that of the entire population, only 1 per cent of fathers are not the "real" parent. Professor Margaret Otlowski, deputy director of the University of Tasmania's Centre for Law and Genetics, said: "I don't think mandatory testing is a good idea. "I can see the argument from the point of view of creating certainty about parentage, but it would stem from a very suspicious premise and there would be huge implications in terms of relationships."