The letter to the bus driver in Horndean, Hampshire, saying he was the father of one Lewis Donnelly of Belfast, born in February 1989 to Louise Donnelly, came out of the blue.
He said he knew nothing about it but his wife Beverley, 32, could not eat or sleep after learning he had apparently had an affair 10 years into their marriage.
He had never been unfaithful, Mr Allen said. 'It was an official-looking letter. Some doubts are bound to creep into your mind even if you trust your husband 150 per cent.'
He rang the agency and told them he had never met a Louise Donnelly, never heard of a four-year-old called Lewis and had never been to Belfast.
The agency rang back later that day admitting it had confused Mr Allen's National Insurance number with another man in the Portsmouth area.
Mr Allen, 33, is now considering legal action. 'My wife was in a state of shock. If we'd got the letter on Saturday and been unable to check it until Monday my marriage would have been in ruins.'
The error was serious because his wife had had a miscarriage two months before the date his alleged son was born. 'When you start accusing people you have got to get your facts right. I've been married 14 years in May and have a 12-year-old son, so it's not as if it was supposed to have happened when I was single.'
A CSA spokeswoman admitted there had been 'a handful' of other cases where men had been mistakenly accused. 'The Child Support Agency very much regrets any distress or embarrassment caused to Mr Allen by the incorrect issuing of a maintenance inquiry form,' she said.Reuse content