Igor Laptev had offered to share his lunch with the youngster after they met at the nearby Soviet embassy, where the young man had gone in a bid to trace his Ukrainian grandparents. After five minutes' small-talk about the teenager's family, education and career aspirations, Laptev gave him his telephone number and promised to try and help.
For Anthony "Alex" Alexandrowicz, the park-bench chat in 1970 was the singular event which he believes destroyed his life.
It was the height of the Cold War and, within a year, Laptev would be expelled from Britain along with 104 other Soviet diplomats. Days after the expulsions, Alexandrowicz was arrested for aggravated burglary. He was given two life sentences and spent the next 22 years in prison - more than double the average term served by a murderer.
"I cannot understand how the Home Office can get away with doing this to anybody," he said when I met him in London. Now 46, but tall and thin, with a grey beard and long hair combed back from his face, he looks aged beyond his years. "I can't sleep at nights because of the flashbacks of what I saw in prison."
He speaks slowly and painfully, stopping intermittently to hold his head in his hands while he waits for the stress to subside. He claims he is innocent of the crime of which he was convicted. Refused a solicitor, denied sleep for 48 hours and told he could not have an identity parade until he made an admission, he consented to sign a police statement although he bore no resemblance to the suspect described by witnesses.
"I had been in institutions since I was 12 and I always did what I was told," he said. "I was scared. I didn't believe they were going to lock me away for the rest of my life."
The crucial factor was the production of a photograph of him and Igor Laptev on the park bench. He said he was warned that his Ukrainian father could be deported if he didn't agree to be "put away somewhere for a while."
Plain clothes officers from Special Branch in Liverpool believed Alexandrowicz was taking messages from the Soviet embassy to his home town of Nelson, known as "Little Moscow" because of its tradition of hard left politics. Alex's father, who had served in the Red Army, had settled there, married an Englishwoman and worked as a labourer.
"My dad was a pretty simple bloke... well, he just wouldn't have done it," said Alex. "I had hardly been home since I was 12, so how the hell could I have been anything?"
The Alexandrowicz household was a violent, unhappy one, and Alex ended up first in care and then in borstal. He ran away to live off his wits in Preston, breaking into houses to steal food and sleeping rough in coal cellars. One break-in led to a year in a young person's prison for aggravated burglary, after a woman opened a front door as he tried to use a pen-knife as a jemmy.
This time, however, he was handed two discretionary life sentences for aggravated burglary and grievous bodily harm, and given Category A security classification. "The other prisoners thought I was a monster. Most people who are given that kind of sentence have been given it for something really serious like murder or child killing."
Shortly after his arrival at Wakefield, then one of the hardest jails in the system, the 18-year-old Alex was cornered in his cell by four prisoners, held down at knife-point and gang-raped. To prevent further sex attacks he later accosted one of his assailants with an iron bar.
Trapped and frustrated inside the jail system, Alex Alexandrovicz the "Soviet spy" contacted the Communist Party of Great Britain and applied to Moscow for Russian citizenship. His hand still bears a fading hammer and sickle tattoo. "I started seeing myself as Russian because they were seeing me as that anyway," he says. Such developments were monitored by the Home Office, along with Alexandrowicz's founding of a prisoners group called the League of Human Rights Observance. The LHRO exposed the practice of using a drug cocktail, known as a "Liquid Cosh", to control difficult inmates.
As he was moved from jail to jail, prison governors, probation officers, psychiatrists and chaplains joined the chorus of calls for his release. Alex recalls: "From 1982, governors would say to me `You shouldn't be here. We don't like locking you up but that's the job we have to do.'" After 21 years in jail with no sign of a release date, Alexandrowicz went on the run from Leyhill prison in 1991 to draw attention to his case. Two years later he was finally set free.
His former prison governor, who has had access to his official files, has come forward in his support.
"At best, this story is the result of the biggest cock-up in the history of the prison service," said David Wilson, now a university professor. "Personally, I am convinced that they believed Alex was a spy. The conclusion that he was a dangerous person who needed to be locked up for 22 years didn't hang true."
Alex now lives alone in Milton Keynes, in a dark one-bedroom flat that looks just like another prison cell. He is too traumatised to venture outdoors much. "I cannot go out of my door. I spent the last ten years in prison down the block (on segregation), and got used to my own company. I can't stop smoking and I'm on constant medication."
When he does go out, he attracts the taunts of local children, who have grown wise to the fact that he is wary of standing up to them, knowing that any breach of his life licence could result in a return to prison.
So he mostly stays indoors, lighting his endless chain of roll-up cigarettes, doing the occasional pencil drawing, and steadily deteriorating in health.
`The Longest Injustice' by Alex Alexandrowicz and David Wilson is published by Waterside Press (01962 855567)Reuse content