That brings the total number of atrocities thwarted by counter terror officers and the security services in the past four months to six.

Ms Dick revealed the latest plot when she gave the annual London mayor's defence and security lecture to an invited audience at the capital's Mansion House.

Previously it had been announced five terror plots had been foiled since the Westminster attack in March – the first of four on the UK that left 36 dead.

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But in her lecture the commissioner said in addition to the '17 weeks of carnage' across London and Manchester 'six attack planning plots were thwarted in the last four months alone'.

''We can expect that figure to rise,'' she said.

Ms Dick said police and MI5 were carrying out 'over 500 investigations into 3,000 individuals across the UK assessed as posing the biggest threats'.

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''There are some 20,000 other former subjects whose risk remains subject to review. I anticipate these numbers will grow,'' she said.

The commissioner urged businesses to support the police by taking their own security measures.

Around 23,000 travel agents across the UK have undergone counter terrorism training to spot potential jihadis heading to or returning from possible Islamic State training in the Middle East, she added.