MI5 had been monitoring the two fanatics responsible for the slaughter of a young soldier near Woolwich barracks for eight years.
The Security Service is facing an inquiry by MPs amid a raft of devastating revelations about the killers’ known links to Islamist extremism.
One of the pair – Michael Adebolajo – was so high profile he was photographed outside Paddington Green police station six years ago behind notorious hate preacher Anjem Choudary.
He was even intercepted by officials as he attempted to travel to Somalia to fight alongside Islamist terrorists last year.
It also emerged that Adebolajo was a violent ex-prisoner who was a member of a banned terrorist group.
Incredibly, he was said to have been preaching jihad on the streets of Woolwich earlier this week, only a few hundred yards from where 25-year-old Army Drummer Lee Rigby – a married father – was beheaded.
As MI5 faced accusations that they let the men slip through the net, David Cameron ordered a full intelligence review by a Westminster committee.