An Islamic State terrorist who plotted to kill Prime Minister Theresa May by taking "her head off" has been jailed for at least 30 years.

Naa’imur Zakariyah Rahman, 21, planned 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 puffa 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.

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

Naa’imur Zakariyah Rahman collected what he thought was a suicide jacket. Credit: Metropolitan Police/PA

On November 1, Rahman was introduced to a member of a fake terror network called Shaq, an undercover police officer, to help him get a blade and suicide vest.

Rahman allegedly told him: “If you can put a belt on me, I’d actually want to do that.”

Jurors were shown covert video footage of a meeting in Shaq’s car in a PC World car park in Brixton on November 6 last year.

In it, Rahman said he would get past the gate, make a “10-second sprint” for the door of Number 10, with his main objective to “take her head off”.

At a further meeting on November 15 last year, Rahman allegedly said: “They’re gonna s*** it, especially her who is inside.”

Rahman carried out reconnaissance around Whitehall, walking past the entrance to Downing Street, and penned an oath of allegiance, the court heard.

He also bought a rucksack in Argos which he gave to Shaq to be fitted with explosives, it is claimed.

A fake bomb that belonged to Naa'imur Zakariyah Rahman. Credit: Met Police

On November 28 last year, Shaq handed him replica explosives, saying it was a powerful device similar to the one used by the Manchester suicide bomber.

Asked if he was ready, Rahman allegedly said: “Yeah. Do you know? Now I’ve seen everything it feels good.”

Rahman was stopped by police as he was walking away carrying a hold-all containing his rucksack and jacket.

He allegedly told officers: “I’m glad it’s over. I’m glad I’m arrested.”

Rahman, from Finchley, north London, was found guilty of preparing acts of terrorism despite claiming he was set up.

During his Old Bailey trial, he admitted to helping a friend to join IS in Libya by recording an IS sponsorship video.

Following his conviction, he told a probation officer that he would have carried out the attack if he had been able to.

Naa’imur Zakariyah Rahman planned to bomb the gates of 10 Downing Street. Credit: Hannah McKay/PA

The “clever and cunning” young man had the potential to “operate below the radar to dreadful effect”, according to a pre-sentence report.

Mr Justice Haddon-Cave concluded: “Rahman is a very dangerous individual and it is difficult to predict when, if ever, he will become de-radicalised and no longer be a danger to society.”

The judge sentenced Rahman to life in prison with a minimum term of 30 years.

For the IS sponsorship video, Rahman was handed six years in prison to run concurrently.

The judge stressed the undercover officers involved in the case were “scrupulous” at all times and Rahman was the “instigator and author” of his own actions.