He has spent 25 years in jail for a murder he denies committing. Even prison governors believe that he is innocent. Will Robert Brown ever be released?

Eamonn O'Neill, investigates.

'This is a perpetual nightmare, I've been left in limbo and words cannot really convey what this experience has done to me," says Robert Brown, a 45-year-old Scot now regarded as the UK's longest-serving prisoner who claims to be the victim of a miscarriage of justice.

The Queen's silver jubilee celebrations were under way the last time Brown tasted freedom. Barely out of his teens, he was arrested, tried, convicted and sentenced for a murder he has always claimed he did not commit. The victim was a 56-year-old woman named Annie Walsh, who was found dead in her flat in Hulme, Manchester, on January 31 1977. Four months later, Brown was arrested. Within a day and a half he had broken down enough to scrawl his signature on a one-page confession that he has always claimed was false.

"In 1977 I'd just turned 20 and I was, like most young men, irresponsible and naive. But after the trial I was suddenly placed in an environment where violence was the norm. To say I had to grow up quickly is an understatement."

Brown's case is now being examined by the Criminal Cases Review Commission (CCRC), the body charged with investigating alleged miscarriages of justice. Officers from the CCRC have been examining the case for 18 months, and for the past three, Brown's lawyer, Robert Lizar, has been repeatedly told that a judgment as to whether his client's case will be referred back to the court of appeal is "imminent".

In the meantime, a high-profile campaign has been launched with support from Helena Kennedy QC, Chris Mullin MP, and former Guildford Four member and now human rights campaigner, Paul Hill. "Brown is really and truly the 'forgotten man' of the British judicial system and police malpractice in the 70s," says Hill, who served a year with Brown in Wormwood Scrubs. "I can tell you that Brown never fitted in in the Scrubs. Everyone knew that this man was innocent. It was a given. The prisoners, the staff, the governor and the visitors - they all knew he'd been fitted up."

In his summing up of the 1977 trial, Mr Justice Milmo stated: "The accused has made very serious allegations not against one police officer only but... against a large number of police officers, and that is probably the principal issue with which you will have to deal in your deliberations when you come to retire." Not surprisingly, the jury chose to believe a team of senior Greater Manchester Police (GMP) detectives over the solitary young man in the dock who constantly protested his innocence and told a story of beatings and coercion. Brown was sentenced to life imprisonment, with a recommendation that he serve at least 15 years. The last thing he shouted as he was led from the dock was, "I am innocent..."

"He was in a terrible state when his father and I visited him in the cells downstairs after he'd been sentenced," Margaret Brown, his 75-year-old mother, tells me. "He was wailing and crying ... He just kept saying over and over again, 'I didn't do it, I didn't do it.'" Margaret Brown is currently lying in a Glasgow hospital after undergoing a major operation for a serious illness. The prison service has twice allowed her son to visit her. Throughout the trips, Brown was chained to a prison warder in case he escaped. This was caught on film by BBC Scotland's Frontline series - the second time in 10 years that I have helped to make a documentary about his case.

I first became involved at the end of 1991 when I was making programmes for Channel 4. I made contact with Brown's lawyer in Manchester and began work on a Scottish Television documentary, which was broadcast in 1993. It led to a petition to the then home secretary, Michael Howard, for an appeal. This was refused.

In the intervening years I have come to know Brown well. We met many times, until the prison authorities tried to make me sign papers guaranteeing that I wouldn't extract information from him about his case: I refused and, with Brown's agreement, suspended prison visits. We have, however, talked by phone almost daily. During this time, governors and deputy governors have written to me expressing their belief in his innocence. I've lost count of the times prison visitors, psychologists and pastoral staff have expressed the same view. All express horror and frustration at how long it takes for someone like him to be exonerated.

Meanwhile, Brown refuses to participate in parole proceedings on the grounds of logic: how can he be paroled for something he didn't do?

When GMP officers arrived at 652 Charles Barry Crescent on January 31 1977, they found a brutal murder scene. Blood was splattered on walls, furniture and ceiling. The postmortem photos reveal 16 small, crescent-shaped injuries, mostly to Walsh's scalp, which caused her massive fatal brain haemorrhage. Later, a Home Office pathologist stated that she had been dead for between two and three days.

The police investigation appears flawed, to say the least. They decided that the motive for the murder was robbery - despite the fact that the victim's handbag, found at the scene of the crime, contained �241. They also claimed that the murder weapon was a lamp in the shape of a woman's head, although one was never found. The evidence of scene-of-the-crime photos - supported by Dr Jim Thorpe of Strathclyde University's renowned forensic department - suggests that a crowbar or metal tool was more than likely used.

None of this, however, is to suggest that the police didn't try to track down the killer. Thousands of statements were taken, and records of local mental hospitals were examined for someone capable of bludgeoning a harmless woman to death.

Annie Walsh was last seen coming home in the late afternoon on Friday 28. One witness, Margaret Jones, claimed that she was with a man. "He was 5ft 3in, very thin and rough looking. He was in his late 20s or early 30s, and had scratch marks on his face... He was white but his hair was shoulder length, Afro-style. It was matted at the back and looked very scruffy."

Within two months she was in a police station looking at a line-up of suspects. She picked out one, a 37-year-old man, but no charges were brought, and he was freed. Eventually, on May 18, the youthful, good-looking Brown was arrested at dawn. At the time he was living with his 16-year-old girlfriend, Cathy Shaw. She later claimed that when the police came, they punched him and threw her naked into a cupboard. Brown has consistently claimed that the arresting detectives did not charge him with murder, read him his rights or offer him a lawyer during the subsequent 32 hours of questioning. He was immediately put in an ID parade and picked out by Jones with the vague words: "He's the only one that looks like him."

Brown claims that later, during questioning, he was punched in the stomach and forced to do step-ups naked on a chair inside Moss Side police station while detectives laughed at the size of his genitals. In 1993, a source showed me a confidential Home Office document, which included a statement from a doctor at Risley remand centre who had examined Brown that May and found "a little tenderness in the area of the sternum and abdomen and could not exclude the possibility that this was caused by blows".

Brown alleges that a GMP serious crime squad detective named Jack Butler played a central role in these violent and abusive proceedings. Later it would emerge that Butler was convicted and sentenced for perverting the course of justice, and corruption in an unrelated case. Another witness has also contacted me in recent weeks, alleging that Butler violently beat him inside a Manchester police station and then allegedly tried to frame him for a robbery in the early 70s. This 63-year-old witness has said that he will testify in Brown's case should it come to the appeal court. When I put to Butler in 1993 the allegation that he had beaten Brown to extract a confession, he said "nothing untoward" had taken place. "I have made it quite clear that... I have no reason to believe that the conviction of Brown is unsound."

The police version is that Brown eventually admitted his guilt after heavy, skilled questioning. Brown claims otherwise. He says that after the beatings, the final straw was when detectives told him that Shaw had said he was guilty. He alleges that he signed the manufactured confession so that he could see her and proclaim his innocence. When they met, Shaw told him that she had never implicated him (she confirmed this to me in several on-the-record interviews before her death in 1993).

During the 25 years that Brown has been in prison, he has lost his father and sister, and is now on the verge of losing his mother. When his sister was dying in 1992, I watched him attempting several times to hug her while chained to a prison officer who refused to unlock the handcuffs. I was ashamed to even witness it. Two days later, she died. He wasn't allowed out for her funeral. "I wept all my tears in private," he later told me. "I'm used to it."