Shortly before 8pm on a wet Monday in April 1979, a police van carrying six officers from Unit 1 of the Metropolitan Police's Special Patrol Group pulled up on Beechcroft Avenue in west London alongside a group of anti-fascist protesters who had been picketing a National Front meeting at Southall Town Hall.
Among the crowd was Clement Blair Peach. Within moments of the police van arriving Mr Peach, a 33-year-old slim, bearded teacher from New Zealand, suffered a blow to the head which fractured his skull and would later kill him.
Bruised but not bleeding, Mr Peach staggered across the road and into a nearby house. When an ambulance called to collect him arrived at 8.12pm, Mr Peach, perhaps not realising the severity of the situation, told paramedics: "My head hurts". Four hours later, at 12.10am, he died at New Ealing hospital.
His case became a cause celebre for campaigners who had often complained about the heavy-handed tactics of the Special Patrol Group (SPG), an elite unit, which came to consider itself as a separate entity within the Met.
It was immediately suspected that a police officer had delivered the blow which killed Mr Peach but it was never proven. A three-decade-long campaign followed, yet, far from secure a prosecution, Mr Peach's family and friends have never even been able to ascertain the exact details of the last moments of his life.
But yesterday a previously unseen police report provided them with closure, of a sort. It revealed that it was almost certainly a policeman who killed Mr Peach and even identifies the officer thought to have delivered the fatal blow.
The release of the documents is bittersweet, however, because, failing a confession, no-one will ever face prosecution over Mr Peach's death.
The report, complied by Commander John Cass, says that his investigation was thwarted by the six officers in the van which pulled into Beechcroft Avenue on that night.
Chief among the culprits was Officer E – the man identified as being most likely to have struck the fatal blow.
Although the report says he was "well thought of with potential for high rank", it adds he was a young officer with "a forceful personality". It was elements of the latter trait which manifested themselves on 23 April 1979. The report paints a picture of an arrogant officer who revelled in the confrontational atmosphere of that night.
One witness said that Officer E got out of the van, waving his truncheon and shouting: "Come on you bastards". It was at this point that 14 witnesses saw an SPG officer hit Mr Peach.
But Commander Cass uses his report to outline the collective amnesia suffered by Officer E and his five colleagues, officers F, G,H,I and J, who found themselves unable to recall any incident that day involving an altercation with Mr Peach – who would have been memorable as one of the only white protesters at the scene. The report describes how, amid the confusion and chaos of a barely-controlled riot, three of the six officers produced suspiciously identical accounts of the day's events, each of them failing to make any mention of the assault on Mr Peach.
Commander Cass wrote: "No officer has admitted striking Clement Blair Peach either deliberately, accidentally, or given an account which would indicate that he may have done so without realising it."
In further interview, Officer E was no more helpful. When it was suggested he must have seen Mr Peach being hit, he replied: "Well I didn't. How much longer have I got to stay?"
Cass also suggested that officers had altered their appearances, growing beards and shaving moustaches, to hamper the investigation by making identity parades more difficult.
Speaking about the actions of the officers with respect to the similar statements and refusal to co-operate, Commander Cass added: "A strong inference that can be drawn from this is that they have conspired together to obstruct police."
The investigation, which was kept from public view for 31 years in the vain hope that a prosecution would materialise, also revealed a worrying culture within the SPG.
An Officer F was suspended after the investigation team found a lead cosh and a whip in his locker. He was also in possession of a stolen driving licence. In an interview he justified possession of the cosh by saying he was a collector of weapons including "Nazi memorabilia" such as bayonets and swords.
Five other officers were found to be in possession of a variety of potential weapons, including a sledge hammer, three knives, wooden staves, a crowbar and three unauthorised truncheons.
Nonetheless, while Commander Cass is critical of the officers who refused to help his investigation, he reveals views which would raise eyebrows if uttered at Scotland Yard today. He suggests that, not withstanding the death of Mr Peach, police can be legally justified in using the most extreme measures in dealing with a riot. Quoting from a legal text, he said: "In case of riot or rebellious assembly the officers endeavouring to disperse the riot are justified in killing them at common law if the riot cannot otherwise be suppressed."