Shiraz Maher, a former member of the radical group Hizb ut-Tahrir, says universities have been wilfully blind to extremist groups recruiting on campus, where they enjoy freedom to operate away from prying eyes.

So, brother, what do you think of 9/11?" asks the man who will later become my mentor. It's just days after the terrorist atrocity and I'm sipping mint tea in his living room.

"Of course, America will use this to wage a war on Islam," he tells me. I wasn't immediately convinced, but was certainly willing to hear more. That was the problem.

Wherever I went, everyone was talking about 9/11. Everyone, that is, except those at the mosques I was attending - they simply buried their heads in the sand.

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I found it frustrating at the time, but now I'm convinced that it was actually quite dangerous, allowing extremist groups such as the one I joined, Hizb ut-Tahrir (Party of Liberation), to seize their opportunity.

After my initial contact with the party, we met quite intensively and I was told I had a duty to "defend Islam" from the impending "humiliation"

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America was about to inflict.

I was told the single most important issue facing the Muslim world was the revival of the caliphate, a theocratic pan-Islamic state uniting all the Muslim lands under a single leader.

It seems absurd now, but at the time it made perfect sense: the party would inspire a revolution "somewhere" in the Muslim world; a caliphate would be declared, and it would then conquer the world.

As a student, I was on the front line. I soon realised just how important universities were for Islamist groups: for young people eager for new ideas they provided an environment far removed from the deadening conservatism of the mosques.

A report leaked last week from the Department for Education and Skills reveals that the Government is issuing instructions to university authorities to monitor radical activities on campus.

The 18-page report warns that universities have become "fertile recruiting grounds", with recruiters "grooming" students for extremism. This is an area where I feel universities have been particularly slow to act and, at times, wilfully blind.

Arab dissidents, including Omar Bakri Mohammed, Farid Kassim and Mohammed al-Masri, first began targeting students in the UK more than a decade ago.

They swamped universities with leaflets declaring "peace with Israel is a crime against Islam" and advised that "the only place for Muslims to meet Jews is on the battlefield". These views quickly attracted the attention of student union officials, who banned them under a "no platform" policy, although this has had little effect.

After the 7/7 terrorist attacks in London last year, Anthony Glees and Chris Pope published an extensive report into extremist students groups, When Students Turn to Terror. Its findings were derided by Universities UK as being inaccurate and alarmist.

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My own experience suggests that the critics should not have been so quick to dismiss the report.

Earlier this year, I met Zaheer Khan while filming a documentary for More4 News. He told me the story of how Omar Sharif, Britain's first suicide bomber, became radicalised while studying at King's College London. He explained how Sharif first arrived from Derby as a well-integrated and confident student excited at the prospect of living in the capital. It was towards the end of his first year that he met Omar Bakri Mohammed - who was still a Hizb ut-Tahrir member at that time.

The changes in Sharif were sudden and dramatic. He soon abandoned his non-Muslim friends, became estranged from society and eventually dropped out of university. When Bakri later ceded from Hizb ut-Tahrir to create al-Muhajiroun in 1996, Sharif followed and Khan lost contact with him.

Khan told me of his despair when he later heard of Sharif's suicide attack in Tel Aviv in April 2003. "I picked up a newspaper, opened it up, and there was Omar's picture, right smack in front of me. I looked at it and thought, 'Oh my God, that's Omar.' Then I started remembering what he was like in his first year, and then I thought, 'My God, things have come to this.'"

The fact that Sharif was never formally a member of either Hizb ut-Tahrir or al-Muhajiroun is largely irrelevant. What matters is that he was set on the path to becoming Britain's first suicide bomber through his initial contacts at university.

His is not an isolated case. The alleged plot to blow up transatlantic airliners over the summer resulted in Waheed Zaman, president of the Islamic Society at London Metropolitan University, being charged with conspiracy to murder.

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While these events continue to attract attention, the more subtle efforts of extremist groups go almost entirely unnoticed.

During the mid-1990s, Hizb ut-Tahrir recruited a large number of students from South Asian backgrounds and has since encouraged them to return to the sub-continent and establish a base for the party there.

"Hundreds of (Hizb ut-Tahrir) members, British but of Pakistani origin, many of them students at the London School of Economics and other centres of excellence, packed their bags and departed for Pakistan," noted Pakistan's Asia Times last year.

It is a point that has generally been missed. Extremist groups use their freedom here to recruit and indoctrinate students in a sheltered environment before sending them back to the Muslim world, where they cause havoc.

In the struggle against violent extremism, we have been quick to charge the Muslim world with neglecting its responsibilities to curb the extremism that thrives in its backyards.

Tony Blair demanded that President Pervez Musharraf move against jihadist outfits in Pakistan after it transpired that two of the 7/7 bombers, Mohammed Sidique Khan and Shehzad Tanweer, visited training camps there.

What he failed to realise is that he has similar duties to curb the radicalism that thrives within our midst.

Just as the 7/7 bombers acquired skills in Pakistan to attack us here, there are scores of recruits from British universities who travel the other way and undermine our allies abroad. The rise in the number of foreign students at British universities in recent years has meant that the effects of this strategy are being felt more acutely now than ever before. These students are overwhelmingly from affluent backgrounds and are likely to have influential contacts in the Army, industry and the Government back home, making them a key target for radicalisation.

Groups such as Hizb ut-Tahrir continue to succeed in attracting recruits primarily because of the increasing sophistication with which they can present their message. They are adept at exploiting the failure of mosques, which perpetuate the biradri system - an unwritten code of social conduct, revolving around honour and deference to "elders" - all of which frustrates the young.

Hizb ut-Tahrir, by contrast, empowers not just young men but, significantly, women too. It accepts female members, encourages them to pursue careers and reject arranged marriages, and it opposes honour killings. Therefore, although the group remains vehement in its rejection of Western values, it is also able to challenge the more reactionary elements of Asian culture.

The group also presents students with an alternative communal identity, neither Western nor Eastern, but based on the Ummah, a global fraternity of the faithful. Its ability to transcend cultural norms and territorial nationalism makes it a seductive proposition.

Universities remain at the heart of all this, and for the most part Islamist groups have operated unchecked. Throughout my time as an activist for Hizb ut-Tahrir my membership was an open secret, and other students even alerted the National Union of Students to it. Despite that, I was able to continue distributing leaflets, organising talks and recruiting students to the cause. The NUS ban was easily sidestepped by creating front societies, and when this became a problem we simply booked lecture rooms under individual names.

The only way to stop this is if university authorities work in tandem with the NUS. But UUK has been reluctant to take action.

Les Ebdon, vice-chancellor of Luton University, defended UUK's inactivity earlier this year by insisting that student bodies such as the NUS are best placed to regulate and monitor events on the ground. He has a point, but this is not in itself enough. The NUS has no control over university facilities and cannot therefore prevent them from being used by extremist groups. Vice-chancellors have an important role to play in preventing their premises from being used for radical activities.

Universities must be careful not to conflate this with the issue of protecting free speech. Radical groups are not interested in an academic dialectic - far from it. Their primary aim lies in recruitment, and their events are nearly always organised with this objective in mind. Sympathetic students are often first identified through these meetings and then vigorously pursued afterwards.

Of course, universities should continue not just to defend academic and intellectual freedom but to promote it.

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But in doing so, they must also accept their wider responsibilities and distinguish between legitimate debate and radical recruitment.

Shiraz Maher is a writer and broadcaster.