THE jury at the trial of a man accused of the murder of a North-East policeman has been told some of those who are due to give evidence took part in the attack and some have even been paid for their co-operation.

Nearly 30 years after Pc Keith Blakelock was killed by a mob yelling "kill the pig" during the first Tottenham riots a man has gone on trial accused of his murder.

Nicky Jacobs, 45, is accused of stabbing Sunderland-born Pc Keith Blakelock, 40, as the officer tried to protect firefighters tackling a blaze at the height of the unrest in on the Broadwater Farm estate in north London in 1985.

A jury at the Old Bailey was told this was the second trial over Pc Blakelock's murder, the first set of convictions being quashed on appeal.

A fresh investigation into the attack led to the decision to give immunity to some people who admitted kicking and punching the officer, with police focusing on those who attacked with weapons, the court was told.

Rather than facing murder charges, some rioters will be giving evidence under pseudonyms because only those "in the inner circle" of the crowd around the officer were close enough to see.

Pc Blakelock's widow, Elizabeth Johnson, from West Boldon, South Tyneside, was at the Old Bailey to hear the opening of the case as supporters of the accused held a protest outside.

Prosecutor, Richard Whittam QC told jurors about the "police dilemma" and warned them to treat the witnesses' evidence with care.

He said they may "strongly disapprove" of their characters, with some having criminal convictions, and drink and drug problems. He also disclosed that some witnesses had been paid rewards for their co-operation.

He told the jury: "Your task is likely to be centred on deciding whether or not you can be sure that these witnesses are telling the truth when they tell you that Nicky Jacobs took part in the attack with a bladed article, acting with others."

Mr Whittam described to the court how the riots erupted on the night of October 6 1985, the day after a suspect's mother, Cynthia Jarrett, had a heart attack and died during a police search of her Tottenham home.

Jacobs was 16, almost 17, at the time of the riot, which followed weeks of tension and concerns that "individuals were planning public disturbances" in the borough of Haringey.

Mr Whittam said: "At least some of the rioters in 1985 appeared to have as their target the death of a police officer.

"Whether that was their primary objective is not something that you will have to decide. The fact is that one police officer was killed and another very seriously injured."

Pc Blakelock was among a group of uniformed officers sent out without cover to protect firemen putting out blazes.

They came across a "very large group of rioters", many armed with an assortment of weapons, the court heard.

"Very heavily outnumbered and fearful they may become trapped both the police and the firefighters were forced to retreat. Outside the flats, as they ran for safety, Pc Blakelock and Pc Richard Coombes went to ground and were set upon to shouts of 'kill the pig' and the like.

"Pc Coombes was very fortunate to survive. Pc Blakelock did not. The attack on him was without mercy. In the ferocious attack his helmet came off.

"He was beaten and stabbed to death before his colleagues were able to force the attackers away.

"Pc Blakelock suffered something in excess of 40 stab type injuries and there appears to have been an attempt made to decapitate him."

Mr Whittam told the jury that the allegation against Jacobs was that he was armed with a bladed weapon and he used it as part of the joint attack on Pc Blakelock.

"There is no dispute that Pc Blakelock was murdered," he said. "There is no dispute that Nicky Jacobs was involved in the public disorder that night, as were some of the witnesses."

Jacobs denies murder and the trial was adjourned until Tuesday.