The Islamist behind the Westminster terror outrage was investigated by MI5 as part of a plot to blow up an Army base using a remote-controlled car, The Telegraph can reveal.

Adrian Ajao, 52, who killed four people, including a police officer in last Wednesday's attack, is understood to have been probed six years ago over alleged connections to four al-Qaeda-inspired terrorists.

Zahid Iqbal, Mohammed Sharfaraz Ahmed, Syed Hussain and Umar Arshad, were jailed for a total of 44 years in 2013 after admitting plotting to launch an audacious bomb attack on a Territorial Army base in their hometown of Luton.

Ajao had moved to the town in 2009 following two stints in Saudi Arabia, and lived just a few hundreds yards from one of the ringleaders.