Duggan was armed and I'll never forget it, says officer who triggered the riots

Police marksman was '100 per cent' certain that suspect had a gun in his hand

Police officers on riot duty in Tottenham in the violent aftermath of the shooting of Mark Duggan (PA)

The police marksman whose shooting of Mark Duggan sparked nationwide riots last summer yesterday described the instant he decided to open fire – saying he was "100 per cent" sure the suspect was armed.

Speaking behind a screen at Snaresbrook Crown Court, the experienced officer, known only as V53, a member of the Metropolitan Police's Specialist Firearms Command CO19 since 2005, said his memory of Mr Duggan emerging from a taxi with a gun on 4 August would "always be in my head".

"The only way I can describe this is it was, if I may, my lord, apologise to the jury, an 'Oh f*** moment'. He's got a gun and he's going to use it on me," he said. He fired two bullets, killing the 29-year-old. The officer was speaking at the trial of Kevin Hutchinson-Foster, who denies providing Mr Duggan with a handgun minutes before he was killed.

The court heard how the police unit had Mr Duggan under surveillance and was tailing him in a minicab between Dalston and Leyton in east London, when he got out of the vehicle "grinning".

The anonymous officer said: "Mark Duggan was holding a handgun in his right hand. He was holding the pistol-grip of the gun. I could make out the shape, the outline, of the gun. I could make out the trigger guard and the barrel. The size of the object he was carrying was of a similar size to the handgun I carry operationally.

"I was aware of previous police incidents in which criminals carry handguns in socks, and there is a black sock covering the firearm Mark Duggan is carrying in his right hand. It is side-on to his stomach."

Just feet away, the suspect appeared to be raising the gun to aim, the officer said: "I had an honest-held belief that Mark Duggan was going to shoot me or one of my colleagues, so I brought my MP5 [sub-machine gun] up to the shooting position." His first round hit the chest. Mr Duggan flinched but was still pointing the firearm at the officer. He continued: "I'm thinking he's going to shoot me or one of my colleagues so I fire a second of my MP5. This has hit him on his right bicep.

"Mark Duggan then fell to the floor. I then closed the suspect down."

Mr Hutchinson-Foster, 30, of no fixed abode, denies "selling or transferring a prohibited firearm" – a modified BBM Bruni Model 92 handgun – to Mr Duggan between 28 July and 5 August, 2011.

The prosecution claims Mr Duggan collected the gun from Mr Hutchinson-Foster in east London, where he placed it in a shoebox.

It was, the Crown says, the same firearm the defendant had used in an attack on Peter Osadebay in a barber's shop six days later. Traces of Mr Osadebay's blood and Mr Hutchinson-Foster's DNA were found on the gun when it was retrieved, while the shoebox was found in the minicab with both Mr Duggan's and the defendant's fingerprints on it.

The trial continues.