The Metropolitan Police has allegedly foiled a plot to assassinate British prime minister Theresa May.
He informed the Cabinet that a total of nine terrorists attacks were foiled by the security agencies in previous year.
Two men have been charged with terror offences and are due to appear in Westminster magistrates' court.
British security services believe they have stopped a suicide bomb plot to assassinate the Prime Minister.
A man died in a terrorist incident at Finsbury Park mosque in north London in the same month - and, in September, an attempt to bomb a Tube train at Parsons Green station failed.
Parker told ministers that United Kingdom authorities had broken up nine potential terrorist attacks over the past year.
Britain has suffered five terrorist attacks this year, in London and Manchester, in which a total of 36 people have been killed.
He said MI5 investigators had misinterpreted intelligence on Abedi. According to a report released Tuesday, authorities missed an opportunity to thwart the Manchester attack. Most terror plots continued to be foiled before they are launched, he said.
It is not clear how Imran and Rahman planned to get through the fortified gates and armed police officers guarding Downing Street. Analysts say the chances of the men gaining entrance to the prime minister's residence would have been remote.
Security measures were introduced in the 1970s but were increased in the 1980s as the threat from Irish republican groups grew. Thatcher was uninjured, but several ministers were seriously wounded in the bombing.