The ex-head of Scotland Yard ordered a covert operation to protect the premier and his wife from the sniper attack during the June 2002 parade to commemorate the Queen’s 50 years on the British throne.
The News of the World, which is serialising Mr Stevens’ memoirs, said the police chief warned the Blairs of the plot, after receiving the intelligence which surfaced only weeks before the event.
But Mr Blair, he said, was “absolutely unfazed” at the potential threat to his life, and both he and his wife vowed to continue to take part, even spurning bulletproof vests.
Mr Stevens said: “I was constantly scanning faces in the crowd for signs of trouble. The fact that nothing untoward did happen was again a tribute to our intelligence gathering and the precautions we took.”