He informed ministers of the plot during the briefing, although the information was held back from the media for several hours.
Both men will appear in custody at Westminster Magistrates' Court on Wednesday (6 December) charged with terror offences. Last week, two men were arrested by armed police and charged with "preparing acts of terrorism".
"MI5 and counter-terrorism policing got a great deal right - particularly in the case of Manchester, they could have succeeded had the cards fallen differently", Anderson said.
The 27-year-old had been watched by MI5. He was seized 90 minutes later in a raid on a house in Birmingham in the English Midlands. Scotland Yard also believe he was trying to join the Islamic State (ISIS) terrorist network. Parker reportedly told Cabinet ministers that British authorities have broken up nine potential terrorist attacks this year.
New blow for Labor as David Feeney hits citizenship hurdle
Attorney-General George Brandis has demanded Labor leader Bill Shorten "do the right thing and refer them himself". But, she said, constant allegations against Senator Gallagher damaged the dignity and standing of the Senate.
He said MI5 investigators had misinterpreted intelligence on Abedi. An official report into the attack released on Tuesday found opportunities to thwart it had been missed. Most terror plots continued to be foiled before they are launched, he said.
An Islamic extremist planned to use an improvised explosive device to blow up the gates of Downing Street before entering No 10 to make an attempt on Theresa May's life.
London Mayor Sadiq Khan, however, said major funding cuts to London police imposed by the central government must be addressed.
Security measures were introduced in the 1970s but were increased in the 1980s as the threat from Irish republican groups grew.