Three thugs picked the wrong victim when they decided to commit a robbery in a railway subway early one morning while armed with a knife.

The man Marvin Joseph, 21, Malacchi Oba, 19, and Mustapha Rahim, 22, confronted at Strood station was a constable on his way to work.

Metropolitan Police officer Kieran McManus identified himself and told them: “Calm down.

“Nothing has happened yet. I will remember your faces.”

They fled but were soon afterwards identified on CCTV cameras as they walked across a bridge to Rochester.

Maidstone Crown Court heard PC McManus went into the subway at about 5am on August 17 last year and a dishevelled woman, believed to be a lookout, spoke to him.

When he reached the end, the three were waiting, knowing it was not covered by CCTV cameras.

Oba brandished a carving knife about 10in long.

Their faces were partially covered. One of them demanded: “Just give us the stuff.”

Prosecutor Toby Long said: “No doubt because of his occupation, Mr McManus stayed calm.”

When he told them he would remember their faces, one replied: “Will you, you?”

They were soon arrested and the discarded knife was recovered by police dog Merlin.

Oba, of Dagmar Road, Chatham, admitted attempted robbery and possessing a knife. Joseph and Rahim, both of no fixed address, denied attempted robbery but were convicted.

Joseph was jailed for four years and three months and Rahim for four years. Oba was sentenced to three years youth custody.

Mr Long said Rahim’s numerous previous convictions included robbery, possessing an imitation firearm and possessing an offensive weapon.

Paul Raudnitz, for Rahim, said once the three discovered the victim was a police officer “standing his ground” the robbery was aborted.

“This was by no stretch of the imagination a sophisticated venture,” he said.

Rahim, he said, was a good boxer and he realised he was wasting precious time in prison.

Nazeem Imambaccus, for Oba, said the teenager was intelligent and articulate but had made poor choices. “It was a selfish and idiotic crime,” she added.

Judge Philip St John-Stevens said it was clear some planning had gone into the offence.

“Presence of mind by Kieron McManus, who announced who he was in terms of being a police officer and keeping calm, managed to dissuade you all from carrying on with the robbery, and it stopped,” said the judge.

“It was fortunate he showed fortitude and presence of mind to stop the matter escalating further.”

Speakign after sentenincing, DC Richard Sears, who investigated the incident, said: "These men thought they would try their luck in the early hours and only ran away when they realised they had targeted a police officer.

"If the victim had been someone else then it may have ended differently so I’m pleased they have received these sentences and that they are no longer on the streets of Medway.