If international terrorism has a global headquarters, it is probably to be found in the barren mountains of Waziristan lining the ungovernable north-west frontier of Pakistan.
Here, British officials believe al-Qa'eda's core leadership, headed by Osama bin Laden and his Egyptian deputy, Ayman al-Zawahiri, has regrouped and found refuge.
North and South Waziristan are two of Pakistan's seven "federally administered Tribal Areas". These barren enclaves on the frontier with Afghanistan are beyond the control of any government, including Gen Pervez Musharraf's embattled regime in Islamabad.
Under agreements first negotiated by the British, the Tribal Areas are run by local chiefs from the Pashtun people and no one else. Pakistani law does not apply to them and no police or security forces are allowed to enter. By tradition, even the army is confined to main roads and agreed outposts. Pakistan has vetoed requests for US troops to enter these areas, where criminals and smugglers have found refuge for centuries.
No better sanctuary for "core al-Qa'eda" could be imagined than this ungoverned expanse of territory covering more than 10,000 square miles of some of the world's most rugged terrain. Moreover, the Tribal Areas have been strongholds of Islamist extremism for decades. Many of the chiefs are natural supporters of bin Laden - perhaps explaining why the American reward of £12.5 million has failed to yield any result so far.
In addition, the chiefs live by the traditional Pashtun code known as "Pashtunwali". Once you accept a guest into your house - and bin Laden has clearly been accepted by somebody - he must be offered absolute protection.
Under American pressure, Gen Musharraf broke with tradition and sent Pakistan's army into the Tribal Areas last year. The only result was fierce fighting and the deaths of at least 600 Pakistani soldiers.
What Blair calls "core al-Qaeda" remains a potent force for evil:
For several years after the terrorist attacks on September 11, they were engaged in little else than avoiding capture and fleeing the American-led offensive in Afghanistan.
Today, by contrast, they are probably secure enough to give strategic direction to al-Qa'eda cells across the world. Once, al-Qa'eda was best thought of as a "franchise" operation: a brand name adopted by numerous terrorist groups operating independently of the key leaders around bin Laden, who British counter-terrorism officials call "core al-Qa'eda".
But this assessment is probably outdated. "Core al-Qa'eda" is believed to have reasserted itself and decided on several key objectives....
While "core al-Qa'eda" gives strategic direction to its followers, it does not exert day to day operational control over them. Bin Laden does not sit in a cave in Waziristan and issue orders for specific attacks on given targets. There is no centralised command structure with bin Laden at its apex.
Al-Qa'eda does not possess an equivalent of the IRA's Army Council where the formal leadership assembles. Instead, "core al-Qa'eda" is a moving circle of people, possibly numbering in the dozens, who give general direction to cells across the globe. In particular, they decide which regions of the world to target for expansion or for attack. So bin Laden and Zawahiri were sporadically in touch with Abu s al-Zarqawi, the terrorist leader who created "al-Qa'eda in Iraq". Until his death last year, Zarqawi seized the chance offered by the Anglo-American invasion of Iraq to open a new front against the western allies.
The spread of al-Qaeda - click here for interactive map
However, it's not all rosy for core al-Qaeda either:
Bin Laden and Zawahiri appear to have spent two or three years after 2001 doing little but evading capture. Western observers often assume that striking America or Europe is their only ambition. In fact, they view toppling Gen Musharraf in Pakistan and overthrowing the Saudi royal family as equally important. Bin Laden sees both these regimes as despicable western puppets. But British officials say al-Qa'eda's decision to attack Saudi Arabia was a major strategic error. After the network carried out a series of attacks on foreign and economic targets in 2003 and 2004, the Kingdom's security forces responded with ruthless efficiency.
At least 2,000 suspects have been arrested - 172 were rounded up in a single operation last month. In Pakistan, Gen Musharraf clings to power, despite al-Qa'eda's best efforts to assassinate him. The general, who claims to have cheated death 11 times, had his narrowest escape on Boxing Day 2004 when a suicide car bomber came within an ace of detonating alongside his limousine. So the "apostate" general is still in office and the Saudi royal family, who have been bin Laden's sworn enemies since they invited US troops into the Kingdom in 1990 and stripped him of his Saudi citizenship, are probably more secure today than they were in 2001.
Elsewhere, al-Qa'eda's efforts to subvert Indonesia, the largest Muslim nation in the world, have been successfully countered. Jemaah Islamiyah, the Indonesian group responsible for the bombing of a nightclub in Bali in 2002, has been crippled by hundreds of arrests and its spiritual leader, Abu Bakar Bashir, is now behind bars.
Neither America nor Western Europe has suffered a mass-casualty terrorist attack since the London bombings almost two years ago. Financing terrorism has become harder and cooperation between the world's intelligence agencies is closer than ever.
Where does that leave us on one side and al-Qaeda on the other?
The key question is whether a new leadership of al-Qa'eda will emerge from the furnace of Iraq. If so, they will probably be more capable than bin Laden's generation, having survived close combat against the most advanced armies in the world. Yet bin Laden is probably as far away from achieving his strategic aims as he was before September 11.
However, America, Britain and all of bin Laden's countless other enemies seem no closer to hunting him down, still less to crushing al-Qa'eda.
The probable truth is that what President George W Bush called the "war on terror" has reached a stalemate. Neither side is close to achieving their goals.
With due respect to David Blair, a hint towards ending the stalemate comes in his description of Musharraf's woes in Pakistan:
Gen Musharraf withdrew his troops from all but a few outposts last September in return for a vague agreement that chiefs would hand over al-Qa'eda suspects and stop the flow of Taliban fighters over the border into Afghanistan. But this deal has yielded little. Some Tribal Areas would be less welcoming than others for "core al-Qa'eda". One, Kurram, has a large population of Shia Muslims with little obvious affinity for al-Qa'eda's brand of Sunni zealotry. Another, Khyber Agency, allows the army to control a chain of border outposts and the main road running through the Khyber Pass linking Pakistan with Afghanistan.
So bin Laden is thought to have headed towards the stronghold of the Waziri tribe in North Waziristan. Safely beyond the reach of both Pakistani and American forces, "core al-Qa'eda" has staged something of a recovery.
It may be necessary for Pakistan's central government to destabilize the balance of power between the Waziri tribe and the other tribes in the Tribal Areas. Perhaps the Waziri tribal leaders must be given a stark choice: expel al-Qaeda and Afghan Taliban elements from your area, or see the other tribes be given the means and the permission to invade Waziristan with the explicit goal of conquest.
UPDATE: Certainly allowing the status quo to continue is not a tenable position for the Pakistani government.
About 100 suspected pro-Taliban militants attacked the house of a government official in northwestern Pakistan before dawn Thursday, killing 13 people, police said.
The house belonged to Ameerud Din, the top administrator of the Khyber Tribal region in North West Frontier Province, bordering Afghanistan.
Din was not home at the time, but his brother, who also is a government servant, was among those killed. Authorities said the dead included six members of the same family and seven guests.
"The attackers fired rockets, threw hand grenades and used guns" for about 30 minutes before fleeing, said Sanaullah Khan, an area police chief.