As British anti-terror police interrogated 11 Pakistanis on Friday over what Prime Minister Gordon Brown called a "major terrorist plot", security sources have indicated that at least three quarters of terrorist plots under investigation in the UK have their roots in Pakistan.
While Afghanistan was seen as the training ground of terrorists in the aftermath of the September 2001 attacks, recent experience has shown that an increasing number of Al-Qaeda extremists are being trained across the border in the tribal areas in north west of Pakistan.
The alleged plot to bomb shopping centres in Manchester during this Easter holiday has been linked by MI5, Britain's intelligence agency, to two Al-Qaeda suspects in Pakistan -- Briton Rashid Rauf and Baitullah Mehsud, the leader of Pakistan's Taliban movement.
An estimated 4,000 British Muslims have been trained in terrorist camps in Pakistan, and with 400,000 British citizens visiting Pakistan each year, there are fears many more will become radicalised, The Daily Telegraph reported.
Monitoring of visitors has intensified, which has raised the possibility of a change in tactics by terrorists, using Pakistani nationals who may not be so closely watched when they visit Britain.
According to the report al-Qaeda was days away from carrying out an "Easter spectacular" of co-ordinated suicide bomb attacks on shopping centres in Manchester.
Police rounded up 12 people, eleven of them Pakistanis in UK on student visa, and some of them were watched by MI5, the British intelligence agency, as they filmed themselves outside the Trafford Centre on the edge of Manchester, the Arndale Centre in the city centre and the nearby St Ann's Square.
Prime Minister Brown has described the alleged plot as "very big" and said that investigators were looking at links with Pakistan.
In talks with the Pakistani leadership, Prime Minister Brown has raised concerns about links between terrorists in the UK and Pakistan and demanded "intensified efforts to crush militants."
He asked President Asif Ali Zardari to do more to root out terrorism emanating from Pakistan's territory after police in the UK arrested a dozen Al-Qaeda suspects, including 11 Pakistanis, over a "very big terrorist plot".
"Prime Minister Brown telephoned President Zardari and the two leaders discussed matters relating to bilateral relations as well as the fight against terrorism," Presidential spokesman Farhatullah Babar said in Islamabad, without giving details.
Earlier, Brown said that there are "links between terrorists in Britain and terrorists in Pakistan. That is an important issue for us to follow through."
"One of the lessons we have learnt is that Pakistan has to do more to root out terrorist elements in its country as well," Brown told Sky News.
Three of the four terrorists who carried out the London suicide bombings in July 2005 were young British men of Pakistani origin. They had travelled to Pakistan to receive religious and military training.
The issue of student visas represents a potential security nightmare for the UK. There are 330,000 foreign students in Britain and around 10,000 student visas are issued every year to Pakistanis alone.
Phil Woolas, the Immigration minister, has described the student visa system as "the major loophole in Britain's border controls".
Wajid Shamsul Hasan, Pakistan's High Commissioner to the UK, told BBC's Newsnight on Thursday night that Britain needed to improve its own system for vetting visa applicants before laying blame on Pakistan.
Asked if there was a problem with the British visa system, he said: "Yes. If they allow us to make inquiries first, if they ask us to scrutinise those people who are seeking visas we can help them. But the thing is they have their own regime."
Britain has been on high security alert ever since the July 2005 attacks in London, which killed 56 people, including four suicide bombers, and failed car bomb attacks in London and Glasgow in June 2007.