Eleven men arrested in raids in the north-west of England remained in detention last night after magistrates gave police a further seven days to question them.
But there are extreme concerns within the security services that there may not be enough evidence amassed to build a case against them, because the raids were rushed forward as a result of Mr Quick's mistake.
The Independent on Sunday has been told by security sources that a number of those being held were identified as possible terrorist plotters by intelligence agencies before they left Pakistan, and were "allowed to run" to Britain through the student visa system, where they were tracked for several months.
Raids were carried out in broad daylight on Wednesday afternoon after Mr Quick allowed a secret document with details of the operation to be in full view of photographers as he left No 10, when he arrived for a briefing with Gordon Brown. He resigned from the force the next day.
Officials, scrambling to avoid a major row, immediately let it be known that the arrests had been planned for 2am Thursday morning, meaning the operation had been brought forward by a matter of a few hours. Yet security sources have told the IoS that the Thursday raid was "only one option" and in fact the planned raid was possibly "several weeks" away.
In a separate development, Sadiq Khan, the minister for community cohesion, said last night that Britain needed to improve the explanation of its foreign policy to Pakistan or risk fuelling anger among young men in that country.
Mr Khan, in Pakistan on an official visit when the raids took place, told the IoS that many young Pakistanis were angry at the US drone attacks on the border region with Afghanistan, and blamed Britain for having too close a relationship with America. He said the Government needed to make clear that UK foreign policy was "distinct" from Washington's.
The minister said: "In Islamabad, I spoke to university students about being British and Muslim: the values we share in the UK and the freedom to practise faith freely, be treated equally, protected against discrimination, and be active citizens with the freedom to voice our concerns and disagree without fear.
"In return, I listened to the anger and pain over the challenges that young Pakistanis growing up in Pakistan face, including the anger and frustration over US drone attacks. It is clear, in many Pakistanis' eyes, the UK is considered in the same terms as the US.
"One of the lessons of the Iraq war is that we need to ensure we are better at explaining our foreign policy, especially when it is distinct and different from [policy in] the US." There were many positive things that Britain and Pakistan shared, such as cricket, added Mr Khan, who was Britain's first Muslim minister.
Although Mr Quick resigned on Thursday morning as assistant commissioner, one intelligence source said he was already "out of his depth" on terrorism issues and it had been only a matter of time before he was replaced. Assistant Commissioner John Yates has taken over the role.
Yesterday, an 18-year-old Pakistani man arrested on Wednesday in the hurried anti-terror operation was released but handed over to immigration officials. Of the 12 men initially arrested, 10 hold student visas and one is a UK-born Briton.
Police yesterday continued to search 10 addresses in Liverpool and Manchester. Officers and forensics teams have been searching properties on Earle Road, Cedar Grove and Highgate Street in Liverpool, and in Manchester on Galsworthy Avenue, Abercarn Close, Esmond Road, Greenhill Road and Cheetham Hill Road.
Officers have seized computers and clothing, but no evidence has been found so far of a bomb-making factory. Some of the suspects had been observed taking photos of shopping centres and a nightclub in Manchester, but without further evidence the case could crumble, say sources.
The current anti-terrorism mission, known as Operation Pathway, is being compared to Operation Crevice, which broke up a plot to blow up nightclubs with huge fertiliser bombs. In that case, intelligence officers waited until suspects obtained the fertiliser before carrying out raids. "It is probable that they [the suspected plotters in the latest investigation] were at the stage of only looking to source material," one source said of the current operation.
The immigration minister Phil Woolas last week denied that security checks for foreign students were inadequate, rejecting claims that the UK would not co-operate with Pakistani authorities over background checks on applicants for visas.
In fact, after the suspects had been identified in Pakistan, it would have been easier for them to be tracked through the student visa system, which would record their movements into Britain, rather than allow them to turn up in the country through other means and become lost in the system.
A security source said the suspects had been watched since before January. One was allowed to enter Britain last week, even though there were irregularities in his paperwork. The Pakistani man was told to return at a later date for an immigration appointment.
The director of a cargo company with access to secure areas inside airports denied reports yesterday that two of the 12 arrested men had worked for him. A van bearing his company's CargoGo logo was seen being pulled over during news coverage of the arrests, but Ian Southworth said police had not been in contact with the firm.
