London (PTI): A Bangladeshi-origin Briton who pledged allegiance to the Islamic State group has been found guilty of hatching a terror plot to behead Prime Minister Theresa May in a suicide attack on Downing Street.

Naa'imur Zakariyah Rahman, on trial at the Old Bailey court in London this week, planned to bomb the gates of 10 Downing Street, kill guards and then attack the prime minister with a knife or gun.

His plan was foiled as a result of a joint undercover operation by the FBI in the US and MI5 and Scotland Yard in the UK. "I want to do a suicide bomb on Parliament.

I want to attempt to kill Theresa May," he is reported to have told the undercover intelligence officers.

"There are lorries here with big gas tankers, if a brother can drive it next to Parliament I will bomb," said the 20-year-old from Birmingham, who had sworn allegiance to ISIS.

He has been on trial along with a 22-year-old ISIS ally, Mohammad Aqib Imran, who is accused of planning to travel abroad either to Libya or Syria to engage in terrorism.