Researchers at St John Moore's University looked at cases of paternity discrepancy over the last 50 years in countries as varied as the United States, Finland and New Zealand and calculated that one in 25 families are affected by the problem.
The rise in cases of teenage pregnancies, sexual infidelity and multiple partners has been highlighted by the study.
Professor Mark Bellis, one of the researchers, claimed that in Britain 20 per cent of women in marriages or long-term relationships have had affairs, and around a third of pregnancies in Britain are unplanned.
The increasing use of genetic testing for medical and legal reasons means that more couples are discovering the biological truth of who fathered their child. An estimated 10,000 paternity tests are carried out each year, many conducted under the scrutiny of the Child Support Agency (CSA) or the courts.
Of the men who demand a paternity test because they suspect infidelity, one in four have their suspicions confirmed.
