Raids to foil an alleged al-Qa'ida bomb plot, hurriedly brought forward after a blunder by a senior police officer, are yet to uncover any explosives or firearms, according to senior security sources. But further pressure was growing on the government last night after after it emerged that the suspects being questioned today may have exploited lax student visa regulations to enter the UK from Pakistan.

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Assistant Commissioner Bob Quick, the Metropolitan Police's counter-terrorism chief, resigned yesterday amid the furore which followed his being photographed carrying secret documents about the anti-terrorist mission to a Downing Street briefing.

Although the details on the document were not published in the British media following a prohibitive Ministry of Defence D-Notice, they appeared on an American website. It forced the police to carry out arrests of 12 suspects and searches of 14 addresses in north-west England in broad daylight, hours before they planned to do so.

Police have taken away computers, literature, maps and clothing from the premises they raided, as well as a car, but they have not, so far, found the bomb-making material needed to carry out the supposedly "imminent" multiple attacks by the suspects.

Greater Manchester Police said yesterday that they were continuing to gather evidence. Chief Constable Peter Fahy acknowledged that it was not ideal that the operation had to be moved forward but added that officers were used to dealing with "fast-moving situations".

According to security sources, some of the suspects had been trailed to pubs and nightclubs as well as shopping centres. However, Mr Fahy said: "There is no particular threat against any particular location ... I would like to say I would have no hesitation, or any of my family, in using any of those locations that have been mentioned."

Senior officers are, however, aware that being forced to move prematurely could have damaging consequences for subsequent prosecutions.

Ten of the 12 arrests on Wednesday were carried out between 5pm and 6pm. Two more men were held from just after 10pm. Eleven of the men hold Pakistani nationality and the twelfth is British of Pakistani extraction. At least seven of the men are said to have entered the UK on student visas and four are believed to have links with the city of Karachi.

According to the confidential briefing document, 10 of those arrested were "student visas Pakistan-born nationals": ie Pakistani citizens studying in Britain. Gordon Brown yesterday called on Pakistan to do more to tackle the "increasing" terrorism links the country has with Britain. The Prime Minister said: "One of the lessons we have learned from the past few years is that Pakistan has to do more to root out terrorist elements in its country as well."

He added: "We know that there are links between terrorists in Britain and terrorists in Pakistan. That is an important issue for us to follow through and that's why I will be talking to President Zardari about what Pakistan can do to help us in the future." Mr Brown defended the police operation, saying: "We are dealing with a very big terrorist plot. We must not forget that the police have been successful in carrying out their arrests ... We had to act pre-emptively to ensure the safety of the public."

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Bob Quick's resignation came after a meeting with Sir Paul Stephenson and the Home Secretary, Jacqui Smith, yesterday morning, when it was agreed the officer would stand down. Sources said it was decided that Scotland Yard would make the announcement, but before they could do so, the London mayor Boris Johnson broke the news on Radio 4's Today programme after being told himself at 7.30am. Home Office sources saccused Mr Johnson of trying to make political capital out of the situation.

Later, Mr Quick said in a statement: "I have today offered my resignation in the knowledge that my action could have compromised a major counter-terrorism operation."

Sir Paul Stephenson, the Scotland Yard commissioner, paid tribute to Mr Quick and said John Yates, formerly the assistant commissioner of the serious crime directorate, has replaced him.

The Quick document: Decoded

The operation

Operation Pathway was, as Mr Quick's note makes clear, secret. It had been in the planning for two months and suspects had been under surveillance. As the note details, it was in relation to "suspected AQ attack planning within the UK". AQ refers to al-Qa'ida and the attacks were said to relate to targets in the North-west. Obvious places such as the Arndale shopping centre and Old Trafford football ground have been mentioned, but not confirmed.

The suspects

The briefing sheet refers to 11 subjects, 10 Pakistanis and one British national. In actual fact the raids revealed a further, unexpected, Pakistan-born national who was also arrested on suspicion of terror offences. The men were aged between their mid-teens and 41 years old.

The addresses

The plan, as detailed on Mr Quick's document, was to make arrests at seven addresses; three by Greater Manchester Police, three by officers from Merseyside and one in Lancashire. After the pictures of Mr Quick were taken the operation was brought forward and only six arrests went ahead as planned: two at a house on Galsworthy Avenue, Cheetham Hill, Manchester, three at Cedar Grove, Toxteth and one at a flat on Earle Road, Merseyside. The others were arrested; one at Liverpool John Moores University, two at a Homebase store in Clitheroe, two at a cyber café in Cheetham Hill Road and one in a white van on the M602 motorway.

The plan

The sheet refers to dynamic entry by firearms teams. This simply means that armed officers planned to raid the homes by breaking the doors down. The raids should have taken place sometime between 2am and 6am yesterday morning as opposed to during Wednesday evening. The reason for this is that suspects are at their most vulnerable when tired and unlikely to fight back. It is also likely they would have been asleep at this time and therefore undressed and unlikely to be carrying weapons.

The command structures

The note reveals the names of all of the senior officers in charge of the investigation – names that The Independent had chosen not to report – including the SIO – Senior Investigating Officer and the three Gold commanders – officers who would be in charge of overseeing the operation in each region.

The media strategy

Also mentioned is confirmation that a plan of what details were to be released to the media, and when, was in place. Like the rest of the details, it too was brought forward when a member of the media – photographer Steve Back – pictured Mr Quick with the supposedly private document.

How Boris took 'Today' by surprise

Transcript from the Today programme

Jim Naughtie: "Bob Quick's future seems to be in the balance this morning – what do you make of it?"

David Winnick MP: "It's obviously very disturbing...(but) I don't believe it's a matter for him to resign or be dismissed."

JN: I'm going to interrupt you there because we've got Boris Johnson, Mayor of London, on the line now. Good morning Mr Johnson. What, as far as you know, is happening at Scotland Yard?

Boris Johnson: "I have this morning with great reluctance and sadness as Chairman of the Metropolitan Police Authority accepted Bob Quick's resignation as head of counter-terrorism..."

JN: "David Winnick, you said you didn't think that this was a resigning matter. Mr Quick has obviously taken the view that he couldn't carry on. What do you make of it?"

DW: "It comes as no surprise. Undoubtedly Mr Quick has done very good work in combating terrorism. We shouldn't forget for one moment, whatever may be the controversy over Mr Quick, that Britain does face an ongoing terrorist danger."

Downfall of a man with Tory enemies

Out: Bob Quick

Like his surname, Bob Quick's tenure as Scotland Yard's head of counter-terrorism was brief. Appointed in March 2008, he resigned yesterday after just over a year in the role.

In that year he was dogged by controversy, and was forced to deal with no fewer than three separate scandals in the final six months of his career.

It was in stark contrast to the rapid rise he enjoyed since joining the Metropolitan Police in 1978. He moved quickly through the ranks, working as a uniformed officer and a detective before being appointed as head of the Yard's anti-corruption unit – a role reserved for officers with unblemished reputations.

A 49-year-old with five children, his profile on the Metropolitan Police website, from which he will soon be removed, lists his interests as skiing, motorcycling and walking. It also reveals that he has a masters degree in business administration from Exeter University and diploma in criminology from Cambridge University.

In 2003 he left the Met to join Surrey Police as chief constable, before returning to the capital as Assistant Commissioner in charge of specialist operations last year. He took over from Andy Hayman, who took early retirement in 2007 amid accusations of lavish expenses and questions over his relationship with a female civil servant – accusations that were later proved unfounded.

Mr Quick's problems started in November when he was named as the officer who authorised the controversial arrest of the Conservative MP Damian Green and the raid on his House of Commons office. He was backed by Sir Paul Stephenson, then Acting Commissioner, but a review raised concerns over the way police conducted the investigation.

The incident blotted his copy book enough to ensure that, when he applied for the Yard's top job late last year, he did not even make the shortlist.

After this a Sunday newspaper revealed that Mr Quick's wife ran a car-hire business from their Surrey home. Critics said that the company website, which showed cars parked outside his house, compromised his security. His reaction compounded the scandal when he accused the Conservative Party of running a media smear campaign against him. He later retracted his comments, saying: "I apologise unreservedly for any offence or embarrassment that I have caused."

That aberration appeared to have been forgotten, although police sources say that Mr Quick has rarely been at work since his outburst.

But yesterday Mr Quick made a final error. Stepping out of a car in Downing Street he inadvertently revealed the details of a sensitive terror investigation. He resigned "in the knowledge that my action could have compromised a major counter-terrorism operation", adding that he deeply regretted the disruption he had caused.

A Scotland Yard source said: "I am not surprised he has gone. If a constable or a sergeant had made the same error they would be looking at serious sanctions, perhaps dismissal. It's an incredibly basic error. For someone in his position to do it is unforgivable. You do not have to be an expert in counter-terrorism to know that you should keep sensitive documents hidden."

Rise of the officer who took on Blair

In: John Yates

As one of the most respected police officers at Scotland Yard, John Yates has a track record so impressive it is easy to see why he was the man the Commissioner turned to in yesterday's hour of need.

In 28 years at the Metropolitan Police, Mr Yates has taken on a number of high-profile investigations, with a good deal of success. Since joining the Met in 1981, after being educated at Marlborough College and King's College London, he quickly progressed through the ranks, as a uniformed officer and a detective, and has led investigations into more than 20 murders.

Between 1999 and 2000 he worked as staff officer to the then commissioner Sir Paul – now Lord – Condon during the Macpherson inquiry into the death of Stephen Lawrence. Other high profile cases he has worked on include the Jeffrey Archer perjury investigation, the Who Wants to be a Millionaire? fraud and an internal corruption inquiry which saw six Met detectives jailed for a total of 46 years.

His only setback of note was in 2005 when, as the officer in charge of the cash-for-honours investigation, he failed to bring a single charge despite interviewing 130 people at a cost of £773,177 to the taxpayer.

The one-year case centred on allegations that House of Lords peerages were offered by Labour and Conservative politicians in exchange for donations to their parties. Despite his confidence that he had built a case that would result in a trial, the Crown Prosecution Service did not bring charges. Mr Yates said his officers received "less than full co-operation".

Despite this, he is still seen as a safe pair of hands by the Met. He was the officer chosen to co-ordinate the British response to the Asian tsunami, for which he was awarded the Queen's Police Medal.

And he was the man who travelled to Brazil to apologise to the family of Jean Charles de Menezes, following the Stockwell Tube operation which saw the innocent Brazilian shot dead. He also stood on the steps of the Old Bailey to publicly apologise for mistakes in the Rachel Nickell investigation which saw Colin Stagg wrongly charged and allowed a murder investigation to go unsolved for 18 years.

A favourite of both the rank-and-file officers and the Met hierarchy, Mr Yates, 50, a keen cyclist who is married with children, was many officers' choice to become Sir Paul Stephenson's deputy when he took the top job earlier this year. But, unlike his fellow Northerner, Mr Yates preferred to stay involved in day-to-day policing.

Yesterday he became the third man in as many years, after Andy Hayman and Bob Quick, to fill the role of Assistant Commissioner in charge of specialist operations. The role gives him national responsibility for counter-terrorism.

A police source said it was easy to see why Mr Yates had been chosen for the job. He said: "He is a top man. Anybody who has worked with him will tell you he is as sharp as a tack. You will rarely come across a more professional officer than John Yates.

"Just sitting in a meeting with him is enough to make you realise that he is much sharper than any of the other officers at his level. His intelligence and ability to grasp things is second to none and he will be great for the counter-terrorism unit. That said, if I was a detective working under him on the serious crime directorate I would be sad to see him go."