Former spy reveals how he foiled a terror plot to kill schoolchildren and parents

A former MI5 officer has revealed how he tracked down an Islamist extremist just hours before he planned to carry out a terror attack on a group of British schoolchildren and their families.

"Tom Marcus" - whose real identity cannot be revealed - has written a book about his time as a surveillance officer which has been cleared by MI5.

This is a clip of an exclusive interview from the Victoria Derbyshire programme.