Naa'imur Zakariyah Rahman, who gave his nationality as Bangladeshi-British, was convicted in London last month of planning to bomb the entry gates to the prime minister's residence at 10 Downing Street. 

Prosecutors said he then intended to kill the guards and to attack May with a knife or gun.

Rahman, 21, who has family in Birmingham and north London, was arrested in November after collecting a backpack he was led to think contained explosives supplied by fellow IS adherents with whom he communicated. He actually had been talking to undercover intelligence agents.

Prior to his arrest, Rahman was referred to a government de-radicalization program, but nonetheless plotted his attack over the course of two years, according to prosecutors. They said two of Rahman's uncles had been jailed in Britain for funding terrorism, while another was killed in a drone strike in Syria.

Judge Charles Haddon-Cave sentenced Rahman to life in prison with no chance of parole for 30 years.

Haddon-Cave said Rahman believed he had obtained a real bomb that was "capable of causing casualties on a scale comparable to those caused at the Manchester Arena," where a suicide bomber at an Ariana Grande concert killed 22 people in 2017.

"Rahman is a very dangerous individual and it is difficult to predict when, if ever, he will become de-radicalized and no longer be a danger to society," the judge said.