Twelve men have been arrested in the north west of England after Britain's most senior counter-terrorism police officer sparked a security alert.
Assistant Commissioner Bob Quick said he "deeply regretted" revealing a secret document to photographers when he arrived for a briefing at No 10.
The document, clearly marked "secret", carried an outline briefing on an ongoing counter-terrorism operation.
The 12 suspects were later arrested at locations across north-west England.
It is understood the raids at eight addresses took place sooner than planned due to the documents being revealed.
Opposition MPs were swift to criticise Mr Quick, with the Liberal Democrats describing him as "accident prone" and the Conservatives condemning his "extraordinary and very alarming" lapse of judgement.
Some hours after the Downing Street incident, two men outside the main library at Liverpool John Moores University were arrested by armed officers from the North West Counter-Terrorism Unit.
Other students said they heard police shouting at the two suspects, then saw them lying face down on the floor.
Student panic
Witnesses said they were advised over the library loudspeaker to stay away from the windows for their own safety.
"Everyone was just panicking," one student told the BBC.
Ten of those arrested are Pakistan-born nationals on student visas and one is a UK-born British national.
Their ages are not entirely known but range between a teenager who is in his mid-to-late teens and a 41-year-old man.
Greater Manchester Police said several hundred officers were involved in the operation, including armed officers during some of the arrests.
Four addresses in the Cheetham Hill area of Manchester, including an internet cafe, are being searched.
Three premises are being searched in Merseyside, plus a guest house in Clitheroe, Lancashire.
Witnesses said two men were taken from the cafe after police arrived.
Mesu Raza, who lives in a flat above the Cheetham Hill cafe, said: "I saw police arrest two people and put them in a police van. They had handcuffs on, they were Asian men, and the police were armed.
"Two police vans arrived outside the shop and there was more police went round the back. There were many officers and a large number of police vans."
The counter-terrorism officers were assisted by officers from Merseyside Police, Greater Manchester Police and Lancashire Constabulary.
Detective Chief Superintendent Tony Porter, head of the North West CTU said: "Today's action is part of a continuing investigation and we have acted on intelligence received.
"Although the operation is ongoing, this phase is still in its very early stages, so the information we can release about it is limited."
Earlier on Wednesday press photographers in Downing Street snapped Mr Quick clutching a white document marked "secret" and containing the names of several senior officers, locations and details about the nature of the overseas threat. Details of the information revealed cannot be reported.
Mr Quick was attending the meeting in his role as lead for counter terrorism and for the Association of Chief Police Officers (Acpo).
On Wednesday evening he apologised to Met Commissioner Sir Paul Stephenson for the slip.
A Scotland Yard spokesman said: "Assistant Commissioner Quick accepts he made a mistake on leaving a sensitive document on open view and deeply regrets it.
Judgement questioned
"He has apologised to the Commissioner and colleagues."
Shadow home secretary Chris Grayling said Mr Quick's judgement had been called into question.
He told the BBC: "The exposure of this document is alarming and quite extraordinary
"The information on the document gave quite a lot of details that was going on. This was highly sensitive information that should not have been carried under an arm in front of a line of photographers."
Liberal Democrat home affairs spokesman, Chris Huhne said: "Assistant Commissioner Bob Quick seems to be increasingly accident prone which is potentially dangerous given the serious responsibilities of his role."
Mr Quick, once seen as a "safe pair of hands" by Scotland Yard colleagues may be becoming accustomed to political controversy.
It was he who ordered the controversial arrest of senior Tory MP Damian Green over alleged security leaks.
He made headlines again last December when he accused the Conservatives of involvement in newspaper stories about his wife's hire car business.
It is not the first time visitors to Downing Street have made the mistake of revealing secret information to the journalists who habitually stand outside No 10.
Last year housing minister Caroline Flint inadvertently showed off secret Cabinet briefing notes revealing a steep projected fall in UK house prices.
