³ÉÈË¿ìÊÖ

A former MI5 surveillance officer who goes by the name of Tom Marcus has described how he nearly killed a man when out shopping.

He told ³ÉÈË¿ìÊÖ Radio 5 live's Nihal Arthanayake and Sarah Brett that he once got suspicious of a couple in Tesco when he was with his wife doing a 'big shop'.

Tom described how the couple split up and went in different directions, and then the man made a phonecall.

He said:
'I'm close enough that I can hear the phonecall and he says 'OK get ready I'm going to do it now', so being involved in a lot of operations where…you seen guys who are going towards blowing buses up or tubes or anything like that you immediately fall into that mindset.'

He described how he then approached the man and what made him stop.

This clip is from Afternoon Edition on Wednesday 5 October 2016.