THE most notorious hitman of the Northern Ireland conflict has told of how he came within three days of assassinating Ken Livingstone.

Loyalist Michael Stone said he planned to "clip" London's mayor in the mid-1980s, when he was leader of the Greater London Council, for his support of the Irish Republican cause.

Posing as a jogger, the former Ulster assassin twice shadowed Mr Livingstone into a Tube station where he planned to shoot him once in the head and twice in the back - "to make sure".

But three days before Stone was due to pull the trigger, several events convinced him that a police informer had infiltrated the operation.

"One of my biggest regrets is that I had to call it off," he said in an interview with the Evening Standard.

At the time Stone had already assassinated at least two Catholics for the Loyalists in Northern Ireland.

He was finally caught in 1988, after television cameras filmed him killing three people and injuring 60 at an IRA funeral in Belfast. The event, later known as the Milltown Massacre, provided some of the most shocking images of the conflict that claimed more than 3,500 lives.

Stone was released from a life in prison under the Good Friday Agreement of 1998, which ruled that those convicted of terrorist crimes were to be set free. He has since become an artist who has sold works for as much as £25,000.

In the 1980s, Loyalists ordered Livingstone's assassination after the politician provoked public outrage by inviting the Sinn Fein leaders Gerry Adams and Martin McGuinness to County Hall.

"Livingstone was the enemy," Stone told the Standard. "He was giving support to people we were at war with and that made him a legitimate target."

The hitman, then 29, came to Britain under the pretence of working as a barman for a Loyalist's hotel in Scarborough. Armed with an intelligence dossier on Livingstone, he travelled into London to carry out two "dry runs".

There, Stone followed Livingstone into Westminster Tube station. "The guy was a gift," he said. "There was no sign of any security at all. He was on his own, with a kind of attache case slung over his shoulder.

"I thought that's how I would do it. I'd clip him on the steps of the Tube."

Stone's hotel contact provided him with a 9mm Beretta pistol, "perfect" for hiding in his tracksuit pocket if he disguised himself as a jogger.

"I decided I would run up behind him when he was on the steps going down, fire one shot into the back of his head, then a double-tap in his torso - to make sure.

"He'd go down head-first and I'd turn around and jog out of the station, towards Embankment, and drop the gun into the river."

Three years ago Stone briefly mentioned in his autobiography, Nothing Shall Divide Us, that there was a plan to eliminate Livingstone. But he only referred to the hitman as "M", not admitting that he himself was to do it.

Stone said he decided to confess only now because an associate from the Ulster Defence Association (UDA) tried to blackmail him over the plot.