James MacLetchie tells why he wants to see a changes to the Child Support Agency after they made his life hell

But since 1996 these were the regular fears that the 47-year-old Gaelic-speaking naturalist, countryside ranger and ghillie had. Despite being infertile, he was pursued to the "point of bankruptcy" by the government's Child Support Agency which insisted that he had fathered a child with his former wife Roberta.

Two weeks ago, his nightmare ended when a sheriff court rejected the CSA's case and declared he could not be the father, setting MacLetchie free from the CSA's "inexorable hounding".

Now, for the first time the North Uist-based naturalist is telling his story and calling for a change in the law to ensure other fathers do not have to go through the same thing.

"I have lost everything I had, and felt so defeated by the injustice, I once contemplated suicide," he says. "I was helped by friends who believed in me and moved mountains to get justice. I managed to maintain my dignity despite a ruthless pursuit by the CSA. That's quite an achievement."

His is a story of intransigence, inflexibility and bureaucracy from a government agency which was not prepared to listen to his side of the story.

MacLetchie came to Uist from Glasgow at the age of six to live with foster parents Maggie and Archie Morrison. "My first memory was being shown a map of the Hebrides in a dark room in Glasgow," he recalls. "These islands are my home."

His new parents were fluent Gaelic speakers. His mother, who died last year, was headmistress at the primary school in Solas and his father was a crofter who worked in the seaweed factory at Lochmaddy.

When MacLetchie married in 1988 his wife Roberta already had two children from previous relationships. Roberta gave birth to a son in 1991.

They were divorced in 1995 and the following year the CSA first contacted him for maintenance payments for Roberta's third child.

MacLetchie knew from the start the child could not be his – in 1987 the couple attended a family planning clinic in Paisley because of their inability to conceive and he subsequently undertook tests at Glasgow Royal Infirmary which revealed he was infertile.

When CSA officials first contacted MacLetchie he was sure medical tests proved he was not the father. His former wife had stayed in their house and kept the car. MacLetchie could see no way to make maintenance payments and failed to respond.

"On occasions when I phoned up the CSA I was told by numerous officers that my protests made no difference and that all monies had to be paid as I had been married at the time and that legally any child born within that marriage made me the presumed father. On hearing this, I became disillusioned and felt there was no hope of opposing their court action. As a result I did not act. The CSA had taken away any optimism."

"It was such a private matter and I felt there was no-one I could turn to on the islands. I did contact solicitors but they either had no family law expertise or refused my case because it was unlikely to qualify for Legal Aid."

In 2003, the CSA arrested MacLetchie's wages and he lost his job as a nature warden three months later. On a remote island there was very limited alternative employment.

"Even if had found another full-time job in the islands, the CSA would have continued to take money from me. I was left penniless and unable to claim benefits. I had to borrow money to survive and got deeper and deeper in debt – finally I sold land that was passed to me by my foster father."

The CSA then placed an order against his home for more than 2,900 in maintenance payments, which meant it could not be sold without the agency taking what it was owed.

Matters came to a head in January 2009 when the CSA raised an action to have MacLetchie jailed for six weeks and his driving licence revoked.

At this point, Brian Keighley entered the story. Dr Keighley is a GP in Stirlingshire and was for 14 years a member of the General Medical Council.

He had spent a week fishing in North Uist every summer since 1987, guided by MacLetchie, who acted as a ghillie. Over the years they became friends.

When MacLetchie told him of the CSA's action, Dr Keighley arranged for MacLetchie to undergo more medical tests at Stirling Royal Infirmary. They showed that unless MacLetchie had suffered some serious – if not miraculous – condition since the 1987 test, he was and always had been sterile. This information was supplied to Lochmaddy Sheriff Court which refused the CSA's application for imprisonment in 2009. But when MacLetchie, Dr Keighley and local MP Angus Brendan MacNeil presented this new information to the CSA, the agency renewed the threat of imprisonment and seizure of assets.

MacLetchie says: "I finally discovered the only way to avoid jail or losing my driving licence was to go to court and obtain a Declarator of Non-Parentage."

After he was refused Legal Aid his only option was to sell his home to pay for legal representation. He then became homeless.

"Had it not been for the kindness of one or two people I would have been sleeping rough," he says.

Finally, two weeks ago a sheriff granted MacLetchie the declarator after his former wife refused four requests to provide DNA samples.

Family lawyer Helen McLean says: "Cases like this are not uncommon – the situation facing men like James is almost impossible. Changes to the CSA are currently being considered which would allow the agency to remove a man's passport as well as his driving licence. This could impact on men in the oil industry working abroad. Obviously a parent caring for children should get support. But James has been forced to virtually bankrupt himself to finance unnecessary court action."

The problem stems from the Law Reform (Parent and Child) (Scotland) Act 1986 and Section 26 of the Child Support Act 1991 which places a duty on the CSA to treat the husband of the "parent with care" as the father when he has signed the birth certificate at registration.

If MacLetchie hadn't signed the birth certificate, or hadn't been married to the mother, the CSA would have needed a court order based on his refusal to provide DNA evidence before demanding maintenance payments.

He offered to take a DNA test – but without a sample from his alleged son it would have proved nothing. Only a sheriff can "draw adverse inference" from the refusal of one party to submit to DNA testing, not the CSA.

His only recourse was to obtain a Declarator of Non-Parentage, something the CSA was not required to make clear to him. Dr Keighley says: "The CSA has pursued a vulnerable man over many years, seeking to have him jailed and his driving licence removed, despite compelling evidence he could never have been the father of his alleged son. He has been left virtually penniless, has lost his home and had his reputation challenged.

"The meeting with the CSA I attended after the second medical examination was unbelievable – they didn't listen, didn't read the evidence and showed no concern that they might be hounding the wrong person. I told them, 'I don't know how you sleep at night'. No evidence we presented made any difference."

The CSA maintains it took action against MacLetchie in an even-handed way. A spokesman for the Child Maintenance and Enforcement Commission (CMEC) said: "Paternity is formally contested in only around 1 per cent of all Child Support Agency cases. The law of presumed parentage, requires alleged fathers married to the mother at the time of birth… to seek a declarator of non-parentage from the courts. While understanding Mr MacLetchie's desire to see a change in the law, the Commission believes current legislation is being correctly applied."

But MacLetchie says: "If a presumed father refuses to take a DNA test the CSA concludes he is the father and forces him to pay maintenance.

"Should the same law not apply in reverse if the mother refuses to take a DNA test – shouldn't the CSA conclude her claim is false without the father having to go through the expense and trauma or court action?

"It has to become compulsory for there to be a DNA test taken on any case where the CSA is seeking payments from absentee fathers and the courts should not entertain any CSA case unless this is produced. Only then, will all I have endured be worth it and the future rights of other individuals be guaranteed."

But MacLetchie is determined not to become embittered.

At last, the pursuit is over.