It's the threat to world peace that dares not speak its name.

We hear plenty about the dangers posed to our security by al-Qa'eda, Afghanistan and Iran. But when it comes to talking about the country that arguably constitutes the greatest threat to our everyday wellbeing, Pakistan hardly ever seems to merit a mention.

This is rather surprising, given that if you talk to any of the military commanders or politicians responsible for prosecuting the war against Islamist terrorism, Pakistan is the country that is almost universally identified as constituting the most serious active threat to our national security.

And it is also seen as the greatest obstacle to our efforts to combat the pernicious threat of jihad by terrorism.

Last week, the subject came up in conversations I had with one of our leading military commanders and a senior politician who is personally involved in the defence of the realm.

About the only response I could evoke from my military acquaintance when I raised the thorny issue of Pakistan was a deep sigh and a shrug of the shoulders. "Ah yes, Pakistan," he said with a world-weary sigh. "A multitude of problems with no obvious solutions."

As for the politician, I was curious as to why the Government seems to have imposed a news blackout on making any statement that might be deemed critical of the Pakistani government. "The fact is, the country is teetering on the precipice of total collapse, and we don't want to be the ones to push it over the edge."

Indeed, the idea of Pakistan replicating the near-anarchy that prevails across the border in Afghanistan is almost too terrifying to contemplate.

While coalition forces have enjoyed much success in eradicating the operational infrastructure of the Taliban and al-Qa'eda in southern Afghanistan, they are deeply frustrated by the fact that the terrorists have simply been allowed to regroup and rebuild across the border in Pakistan's lawless tribal areas.

British military commanders last week told The Sunday Telegraph that the five-fold increase in roadside bomb attacks in southern Afghanistan was the result of the training that Taliban fighters were receiving at religious schools in Pakistan, where they are being taught to make explosives and build improvised explosive devices.

And while al-Qa'eda is not the force it was when it carried out the September 11 attacks, Western intelligence experts believe the core of al-Qa'eda's leadership - possibly including Osama bin Laden himself - is based in the inhospitable mountain ranges of Waziristan in Pakistan, where they continue to plot their diabolical schemes to attack the West.

To this potent Taliban/al-Qa'eda terrorist mix has now been added the new ingredient of Pakistan's home-grown Islamist radicals, which Western security experts call the Pakistani Taliban to distinguish them from their Afghan neighbours.

The Pakistani Taliban is made up of indigenous Muslims who have been radicalised in one of the hundreds of Saudi-funded madrassahs, which openly preach that young Muslims have an obligation to wage Jihad against the infidels of the West.

Nearly all the major terror plots against Britain - both those that succeeded, such as the July 7 bombings, and those that have been foiled by the vigilance of our security services - have been linked in some way to Pakistan.

The emergence of a new, home-grown terrorist organisation in Pakistan has dramatically increased the threat the country poses to Britain.

As if this wasn't enough to give us all sleepless nights, Pakistan is the only Muslim country known to possess a nuclear weapons arsenal.

So long as President Pervez Musharraf remains the country's titular head, the West has some degree of assurance that Pakistan's nukes remain secure for, in his former capacity as the head of Pakistan's armed forces, Musharraf allowed US officials to make sure the necessary safeguards were in place to ensure the nukes did not fall into the wrong hands.

Al-Qa'eda's training manuals make no secret of the fact that the organisation would love to get its hands on a nuclear device, and the only two likely places it could do this are Pakistan and Iran.

Dr Abdul Qadeer Khan, the "father" of Pakistan's nuclear weapons arsenal, spent the Nineties making a tidy profit from hawking his nuclear-bomb blueprints to some of the world's less stable regimes, and North Korea, Libya and Iran were among some of the more notorious beneficiaries.

Although Dr Khan was placed under house arrest after his activities were exposed by Western intelligence agencies in 2002, Pakistan's new coalition government, bowing to nationalist pressure, has indicated it is prepared to rehabilitate the disgraced nuclear scientist, even though the West is still struggling to come to terms with the consequences of his clandestine nuclear proliferation network.

This is just one of several disturbing developments to emerge from Pakistan since the new coalition government took power earlier this year, in reaction to the West putting pressure on Mr Musharraf to return the country to democratic rule.

At the time, both London and Washington believed that Pakistan having a democratic government would increase its co-operation in fighting terrorism. In fact, the opposite appears to have happened.

The West might have been frustrated by what it perceived as Mr Musharraf's lack of commitment to rooting out terror groups in Waziristan, but at least while he was directly running the country there were sporadic bouts of activity.

But talk to any of the military commanders involved with prosecuting the war against the Taliban and al-Qa'eda, and they will tell you that Pakistani co-operation has virtually ground to a halt since the coalition government took control.

Until now, the West has maintained a discreet silence about its concerns regarding Pakistan's lack of commitment to rooting out Islamist terror cells, hoping that the new government in Islamabad can be persuaded to mend its ways. But the West's mounting frustration is unlikely to be contained for much longer.

Barack Obama, the Democrat presidential nominee, last week became the first leading Western politician to voice his frustration with Islamabad when he declared that he would have no hesitation in ordering American troops to pursue terror suspects across the Pakistani border "if Pakistan cannot or will not act".

The Pakistanis ignore this shot across their bows at their peril.