On the 21st anniversary of the murder of the Muswell Hill policeman, Keith Blakelock, Chief Superintendent Simon O'Brien, Haringey's top policeman, said there are still lessons to be learnt from PC Blakelock's death.

During the annual wreath-laying ceremony at a specially consecrated memorial in Muswell Hill Broadway, on Friday, Chief Supt O'Brien, who led the tribute, said it was very important the community and police worked together to prevent a repeat of the incident.

Sunderland-born father of three, PC Blakelock, a Muswell Hill community policeman, was hacked to death by a mob on October 6, 1985, during riots at the Broadwater Farm housing estate in Tottenham. The attack was sparked by the death of Cynthia Jarrett, who collapsed during a police raid on her home. The level of violence was such that the police were forced to withdraw, but when retreating, PC Blakelock fell and was set upon with machetes and knives. He was posthumously awarded the Queen's Medal for Bravery.

Three London men were convicted of his murder in 1987 but were cleared four years later, on appeal, after claims that the evidence used in the case had been fabricated.

As is tradition, the youngest Haringey police officer laid the wreath at the memorial on Friday, and the ceremony, in the autumn rain, was attended by all new borough recruits.

Chief Supt O'Brien said he believed it was vitally important that the young officers witnessed the ceremony to better understand the tragedy.

He said: "We lost one of our colleagues in the worst circumstances.

"There are many great times in the force but this is one of our darkest and I think it is right that we continue to learn from this lesson."

The investigation into PC Blakelock's murder remains open.