The sergeant in charge of PC Keith Blakelock's unit has told a murder trial of the "absolutely terrifying" moment police officers came under attack by a mob with iron bars and a machete.

David Pengelly told the Old Bailey, London, how he led his team of 10 officers to protect firefighters tackling a blaze at a supermarket on an upper deck of the Broadwater Farm estate in Tottenham, London.

Mr Pengelly gave his "nightmare" account of the night of October 6, 1985 at the trial of Nicky Jacobs, 45, who is accused of murdering PC Blakelock, 40.

Mr Pengelly told how his team, serial 502, were not "shield trained" at the time, but nevertheless kitted themselves out in fire protective boiler suits, visors and long and round shields before going to the scene.

When they arrived, he said: "It was a scene of considerable disorder. There were lines of officers with shields. There were missiles being thrown. It was a scene of considerable rioting."

As the team went with firefighters, it was PC Blakelock who suggested someone should stay by the stairwell to protect their exit, which he and another officer then did.

Mr Pengelly said: "I saw a group of youths. My eye was drawn to youths who were running underneath us." One rioter he noticed had muslin covering his face, with eye holes cut into it, he said.

Some of the youths started to run around to "effectively out flank us and cut off our retreat" so Mr Pengelly gave the order to retreat down the stairs to the ground level.

"Obviously at this point, the rioters were right with us hammering on the shields. It was an absolutely terrifying scenario.

"As we retreated down the stairway there were people with iron bars and at least one with a machete, effectively trying to chop the shields to bits. The retreat to ground level was a continuing nightmare."

The trial continues.