A senior judge hailed the “extraordinary” investigation which brought an  Islamic State terrorist to justice for a plot to kill the Prime Minister Theresa May.

Naa’imur Zakariyah Rahman, 20, could be facing life behind bars for planning to bomb the gates of 10 Downing Street, kill guards and then attack Theresa May with a knife or gun.

He had pledged allegiance to IS and collected what he thought was an explosives-packed jacket and rucksack when he was arrested last November.

The drifter, originally from Birmingham, thought he was being helped by an IS handler when in fact he was talking to undercover officers.

Following an Old Bailey trial, Rahman, from Finchley, north London, was found guilty of preparing acts of terrorism in Britain.

Midway through the trial, he admitted helping his friend Mohammed Aqib Imran to join IS in Libya by recording an IS sponsorship video.

Trial judge Mr Justice Haddon-Cave said the evidence against Rahman was “overwhelming” as he adjourned sentencing to August 31.

He said: “Mr Rahman, you have been found guilty of these serious charges by this intelligent and hard-working jury who has seen through your web of lies.”

The defendant mumbled “thank you” before being led from the dock.

The senior judge also paid tribute to the way the “extraordinary” case had been “robustly investigated, prepared and presented”.

He added that it would be “extremely reassuring for the public as to how this remarkable investigation has been conducted”.

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Naa’imur Zakariyah Rahman planned to attack Theresa May with a knife or gun (Stefan Rousseau/PA)

Rahman was snared by a network of undercover counter-terrorism officers from the Metropolitan Police, the FBI and MI5.

Deputy Assistant Commissioner Dean Haydon, from Scotland Yard, said: “His intention was to go to the gates of Number 10.

“He was going to detonate one of the devices that would have killed police officers and members of the public.

“His intention was then to go on through the gates of Number 10, detonate potentially another device there which would get him into Number 10, then, having a knife or gun, attack the PM.

“He was expecting to die in the process and essentially commit martyrdom, detonating a bomb in central London at the heart of Government.

“If he had got hold of a genuine bomb, a gun, or a knife, we would have been talking about an individual who could have killed, injured and maimed a number of individuals in Whitehall.”

His IS sponsorship video would have provided “great gravitas” if he had gone through with his martyrdom plan, Mr Haydon added.

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Naa’imur Zakariyah Rahman is caught on CCTV at Digbeth coach station, Birmingham (Metropolitan Police/PA)

The trial had heard how Rahman was encouraged by an uncle who travelled to Syria to fight and was killed in a drone strike last June.

Two other uncles had been jailed in August 2016 for funding terrorism.

His concerned mother had moved to north London to get away from their influence, and Rahman was referred to the de-radicalisation Channel programme.

But Rahman spun a web of lies to Channel and went on to plot his attack over the course of two years.

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Court sketch of Naa’imur Zakariyah Rahman (left) and Mohammed Aqib Imran in the dock (Elizabeth Cook/PA)

Rahman came to the attention of police in July last year when he complained he was being blackmailed, but failed to attend an appointment.

In August last year he was arrested on suspicion of sending indecent images to underage girls, but never charged.

An examination of his mobile phone raised concern he may be harbouring extremist views.

After his uncle’s death, he became even more determined and turned to the internet for help in his attack plans.

Rahman made contact with an FBI agent posing as an IS official online, who introduced him to an MI5 role-player.

The defendant revealed his plans, saying: “I want to do a suicide bomb on Parliament. I want to attempt to kill Theresa May.

“There are lorries here with big gas tankers, if a brother can drive it next to Parliament I will bomb.”

He later described using a suicide belt, a drone, an IED and poison, referred to as “P” or “curry mix”.

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Rahman’s jacket was fitted with dummy explosives before his arrest (Metropolitan Police/PA)

By early November last year, he appeared settled on an attack on 10 Downing street with a suicide bomb, gun or knife.

He told an undercover officer: “(God willing) will be very big if I’m successful. I can’t mess up. I can’t get (martyrdom) if I get caught.”

On November 18 last year, Rahman carried out reconnaissance around Whitehall.

Two days later, he bought a rucksack from Argos before meeting an undercover officer in Brixton for it to be fitted with explosives.

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Naa’imur Zakariyah Rahman bought a rucksack from Argos to be fitted with explosives (Metropolitan Police/PA)

On November 28 last year, the officer handed back Rahman’s rucksack and coat, now packed with dummy explosives, and replica pepper spray.

Rahman told the officer he was “good to go” but was arrested as he walked away carrying the fake bomb, in Kensington.

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The device belonging to Naa’imur Zakariyah Rahman (Metropolitan Police/PA)

Rahman was paranoid about being caught by police but never suspected that he was talking to undercover agents online.

In his defence, Rahman claimed he had been set up by security services online, but a jury rejected his explanation and convicted him after 13 hours of deliberations.

Rahman’s co-defendant Imran, 22, from south-east Birmingham, was found guilty of having a terrorist handbook.

But on Thursday, after more than 15 hours of deliberations, jurors could not agree on a verdict on a charge against Imran of preparing terrorist acts abroad.

The jury was discharged and prosecutor Mark Heywood QC said the Crown would be seeking a retrial in his case.

Sue Hemming, from the Crown Prosecution Service,  said: “Naa’imur Rahman planned a terror attack at the heart of British democracy.

“Despite the evidence against him including recordings of incriminating conversations, he denied preparing to commit a terrorist act.

“Thanks to the work of the police and security services, he would never have succeeded.

“The prosecution was able show that he posed a serious danger to the public and was a committed jihadist who accepted Daesh’s violent propaganda without question.”