A 35-year-old man who spent 15 years in jail after being convicted of murder on the sole evidence of a confession that he had made had his conviction quashed by the Court of Appeal yesterday.

Three judges unanimously agreed with lawyers for John Roberts that his confession to the crime when he was 19 was unreliable because new psychiatric evidence had shown that he was then in a vulnerable mental condition and tended to be compliant with people in authority.

As his conviction in 1983 for murdering Daniel Sands, 41, a farmer, was based solely on his confession, the judges, headed by Lord Justice Henry, ruled that it was unsafe and must be quashed. Mr Roberts was released on licence last year after his case was referred back to the Court of Appeal by Jack Straw, the Home Secretary.

He was in court with his mother, Rose, yesterday to hear Lord Justice Henry, who was sitting with Mr Justice Ognall and Mr Justice Toulson, say a "grave injustice" had been done. Lord Justice Henry said: "We are conscious that the unreserved apology we offer him for it, and our profound regret that it should have occurred, will not give him back those lost years of life and liberty."

He said: "Medical science and the law have moved a long way since 1982. We hope that the safeguards now in place will prevent others becoming victims of similar miscarriages of justice." Mr Roberts' confession to West Mercia police was made within hours of his arrest at his home in Shrewsbury after the decomposed body of Mr Sands was discovered in a shallow grave at Barleycorn Farm, Grinshill, Shropshire.

Mr Sands, who had been shot in the head, had been missing for 18 months. In February 1983, Mr Roberts and Richard Evans, then 23, were convicted of the murder. Mr Roberts was detained during Her Majesty's pleasure, and Evans was given a life sentence.

Quashing Mr Roberts's conviction yesterday, Lord Justice Henry said it had been based solely on his confession. Since then, medical science and the law knew much more about the phenomenon of false confessions, the judge said. In the light of the medical evidence, which had not been put before the trial court, the confession should not have been admitted in evidence and, without the confession, there was no case against Mr Roberts.

Outside the court, Mr Roberts said it taken him until 1988 to find lawyers who were prepared to take on his claim that he had been wrongly convicted. He said: "Basically the police really intimidated me and badgered me constantly. No matter what I said, they were saying something else. At the end of the day, I really gave up, as no one was listening. But I knew the truth would out anyway - it has a nasty way of doing that."

He no longer felt bitter about his experience and had picked up the strands of his life, working for an uncle in Shrewsbury. His solicitor, Safina Din, said the family was gratified that justice had at last been done. The possibility of a claim for compensation was being considered.

Mr Roberts had claimed that he and Evans had been working at the farm and that, when he arrived one morning, Evans told him that Mr Sands was dead in the kitchen. He had helped Evans to bury the body because he was frightened. In his judgment, Lord Justice Henry said that the police interview with Mr Roberts took place before the safeguards for suspects under interrogation had been introduced by the 1984 Police and Criminal Evidence Act.

The situation had also been changed by the development of psychometric tests, which the medical profession - and latterly the courts - accepted as capable of providing a measure of suggestibility. There was an element of truth in the Crown's "forensic over-statement" that the position in 1982 resembled the "dark ages", said the judge. A report by a clinical psychologist in August 1994 had triggered the Home Secretary's decision to refer the case for review by the Court of Appeal.

The novelty of the psychologist's task had been to conduct a retrospective assessment of Mr Roberts's susceptibility in 1982 to making a false confession and she had concluded that his type of false confession was the "coerced-compliant" type. All the expert evidence agreed that Mr Roberts had an excessively compliant personality and, consequently, was vulnerable.

Lord Justice Henry said that Mr Roberts had "pre-eminently" needed the attendance and support of a solicitor at the time he was being questioned by the police and there were no grounds for holding him incommunicado, as he had been for a time. If the new evidence had been before the trial court, the judge would have been bound to exclude the confession and, without it, there was no case to go to the jury.