

He applied for a visa to visit disabled groups here and for no reason anyone can comprehend, the authorities turned him down.

The voice of Murtaza Ali Shah, London correspondent of Pakistan's Daily Jang, is incredulous when he asks how his friend could be a threat. It turns astringent when he moves on to the arrest of the Pakistani "terror suspects".

Shah was flabbergasted that politicians and the media could accuse them of planning mass murder when there was not the evidence to convict them or to bring them to court or even to charge them. That Britain will now deport the students, as if they were somehow guilty anyway, emphasises the precariousness of his own life.

To Shah, and other recent Pakistani immigrants, the arrests change the way they feel about Britain, makes them think they are becoming enemy aliens in their adopted country. The Daily Jang is a progressive paper and Shah has no time for Islamism, but he told his readers that "the scare of a terror attack is such a phenomenon in Britain that even a cracker on the street corner could go on to become headlines".

I did not have the heart to tell him that the paranoia will deepen as British politicians struggled to come to terms with a Pakistani civil war.

I do not know if the crisis is making a few of the sophisticates who used to jiggle their fingers and put postmodern quotation marks around the so-called war on terror think again. I know for a fact, however, that fear has been spreading through Whitehall ever since Pakistan paid its version of Danegeld and allowed the Taliban to tyrannise the 1.7m citizens of the Swat Valley in return for illusory promises of peace.

The government knows that the fates of Pakistan and Britain are entwined. If Hillary Clinton is proved right when she said that "by abdicating to the Taliban and the extremists" the Pakistani elite fuelled an "existential threat" to its own state, then the consequences for Britain will be extraordinary and not merely because of the effects on the Pakistani diaspora in British cities.

Most people understand that the danger of terrorist atrocities will rise as Islamists establish new training camps for jihadis from Britain and Pakistan. Politicians are as worried about waves of refugees from a civil war.

Of the figures I spoke to, only the former foreign minister Denis MacShane rejected hopelessness. As always, he was fizzing with social democratic responses to the crisis. We should end the use of "Af-Pak" to describe the war against Islamism in south Asia. Not only is it an ugly and faintly racist - would we call tensions between China and Japan "Chink-Jap?" - but it misses the true nature of a triangular conflict. The Pakistani elite is obsessed with the threat from India not Islamism. We should therefore put pressure on India to temper its hostile stance and give Pakistan the time to confront the internal menace. While we're at it, we should redirect the aid budget so it funded schools, particularly girls' schools, in Muslim countries and tackle the power bases of the religious far right in British universities so that moderate Pakistanis were not radicalised here.

On he went and I agreed with every word. Tellingly, though, he was the only senior figure who would speak on the record. Off the record, others concluded it was a little late to be building schools or making probably futile attempts to lessen Indo-Pakistani tensions.

One senior figure involved with terrorism strategy put it like this: "If Pakistan continues to descend into chaos, movement between our countries will slow extraordinarily quickly. There will be queues of tens of thousands waiting for visas. SIS [that's MI6] will stop trusting the information they get from the Pakistani intelligence services and we will not clear people for visits."

As most visitors from Pakistan are relatives seeing their families, the effect of a clampdown on everyday life for British Pakistanis would be severe, but it would be as nothing in comparison to the draconian system awaiting refugees. Without me attempting to put words in his mouth or asking a leading question, one influential figure began to muse on the possibility of closing the borders.

Women, Christians, Sufi Muslims and democrats are already fleeing the advancing Taliban. If war drives them to think of seeking asylum here, the government is considering the introduction of a discriminatory visa system to stop them reaching Heathrow. "We would have to amend the Race Relations Act and possibly opt out of the Human Rights Act if we wanted a special visa system that applied only to Pakistan but not other countries," said my source, who gave every impression he was considering doing both.

I thought it outrageous to contemplate stopping, say, a Pakistani women's rights campaigner from finding sanctuary from the most murderous misogynists on Earth and I am sure a part of him did too. I wondered what the Zahid Abdullahs and the Murtaza Ali Shahs would make of repression. He did not know the answer to that either.

All he knew was that Britain could not cope with either Swat-trained terrorists or hundreds of thousands of refugees. "Pakistan is what is keeping me awake at night," he said with a voice close to despair. He is not alone in that.