Senior members of al-Qaida are feared to be moving to North Africa to open up a new front after being weakened in Pakistan. Senior British officials believe that a "last push" in 2012 is likely to definitively destroy al-Qaida's remaining senior leadership in Pakistan, opening a new phase in the battle against terrorism.

So many senior members of the organisation have been killed in an intense campaign of air strikes involving missiles launched from unmanned drones that "only a handful of the key players" remain alive, one British official said.

However, well-informed sources outside government and close to Islamist groups in north Africa said at least two relatively senior al-Qaida figures have already made their way to Libya, with others intercepted en route, raising fears that north Africa could become a new "theatre of jihad" in coming months or years.

"A group of very experienced figures from north Africa left camps in Afghanistan's north-eastern Kunar province where they have been based for several years and traveled back across the Middle East," one source said. "Some got stopped but a few got through."

It is unclear whether the moves from west Asia to North Africa are prompted by a desire for greater security – which seems unlikely as Nato forces begin to withdraw from Afghanistan – or part of a strategic attempt to exploit the aftermath of the Arab spring. They may even be trying to shift the centre of gravity of al-Qaida's effort back to the homelands of the vast majority of its members.

Since the death of Osama bin Laden in a US special forces raid in Pakistan last May, other senior leaders have also been eliminated, even though the numbers of strikes are lower than last year.

The problems for al-Qaida in west Asia have been compounded by a smaller flow of volunteers reaching make shift bases in Pakistan's tribal zones. "I think they are really very much weakened," said the official. "You can't say they don't pose a threat – they do – but it's a much lesser one."

British and US intelligence sources have told the Guardian newspaper they estimate that there are less than 100 "al-Qaida or al-Qaida-affiliated" militants in Afghanistan, of whom only "a handful" were seen to pose a threat internationally to the UK or other western nations.

Officials dealing with Afghanistan and Pakistan say they see al-Qaida's activity as "effectively marginal" to events there. Instead, local networks, such as that run by the Haqqani family in the semi-autonomous tribal agency of North Waziristan on the Afghan-Pakistan border, are deemed more important.

Though the hunt for Ayman al-Zawahiri, the veteran Egyptian militant strategist who replaced Bin Laden as leader of al-Qaida, is a top priority, western officials say there is equal emphasis on eliminating those immediately below him in the now somewhat chaotic hierarchy.

These include Saif al-Adel, an experienced operator who may have returned to Pakistan, and Abu Yahya al-Libi, a Libyan in his mid-40s who escaped from a US prison in Afghanistan and has featured in propaganda videos.

Few doubt that al-Qaida is evolving. "Al-Zawahiri's leadership is transitional and he is handicapped by his own old school background. We are waiting to see what a new al-Qaida might look like," the official said.

Overall, analysts say, the picture is one of fragmentation, with groups in Somalia, Yemen and elsewhere pursuing local agendas.

In Europe, security services say levels of radicalisation have stabilised. Analysis of a list of "recent martyrs" published by the Islamic Movement of Uzbekistan, which shares al-Qaida's ideology and is also based in Pakistan's tribal areas, appears to show that fewer number of Europeans than feared reached the group, previously been favoured by German-based extremists. Of the near 100 listed, only one was German and most appeared to be local men.

The move to Libya is seen as particularly alarming. William Hague, the foreign secretary, recently warned that mercenaries driven out of Libya could switch allegiance to al-Qaida in the Islamic Maghreb. While this seems unlikely, sources in Libyan mainstream Islamist groups say there is evidence of grassroots activism by individuals linked to al-Qaida that could lead to new cells being formed.

In a recent communique, Zawahiri made a particular appeal to Libyan fighters not to lay down or hand in their weapons. (The Guardian)