The Streatham attacker had been under surveillance for more than a week before he stabbed two people

The Security Service stepped up surveillance and drafted in armed officers 48 hours before the Streatham attacker stole a knife and stabbed two people.

Sudesh Amman had been under surveillance for more than a week but his visit to the shop from which he started his attack prompted MI5 and counterterrorism officers to step up the operation to contain him.

Amman, 20, stabbed a man and a woman on Streatham High Road last Sunday and was shot dead by officers.

He was thought to have been “scoping out” the shop on his first visit and reports that the shop was already a concern will raise questions about how he was able to grab the 10in ceramic-coated knife, tear off the packaging and stab two people