Some senior western officials now suspect the Haqqani network of carrying out the September 20 assassination of Burhanuddin Rabbani, the chairman of the Afghan High Peace Council. These suspicions are based on circumstantial rather than hard evidence, and that is why no public announcements have been made. There is also confusion over whether the hit was ordered by the Taliban leadership, and this confusion may extend to the Taliban itself judging from its muddled response to the killing.

The killing of Rabbani was a huge setback in the bid to get peace talks going. If it turns out it was ordered by the Quetta Shura, that effort would be shelved for the foreseeable future. The mood is tangibly darker in Whitehall than a few weeks ago. A planned review of progress in Afghanistan, ordered by David Cameron in the summer, is due to be completed in the next few weeks and it is expected to raise the spectre of a slide into civil war or the Talibanisation of the Pashtun belt straddling the Afghanistan-Pakistan border.

The outcome could be far worse than the turmoil of the 1990's, officials fear, because Pakistan is now much less resilient that it was then, and could be consumed by the spread of instability. This remains a worst-case scenario. More likely, British officials believe, is a precarious region chronically marred by pockets of violence after western combat troops leave in 2014. But even this outcome would represent as big a national security threat to the UK as it does today, not to mention continued misery for the people who live there.

The facts of the Rabbani killing will have an importance influence on the political trajectory from here. The circumstantial evidence pointing to the Haqqanis includes (but is not limited to) the belief that the style of assassination bore the hallmarks of the North Waziristan-based clan and its al-Qaida allies, and the fact that the member of the High Peace Council (HPC) who introduced the assassin to Rabbani was Rahmatullah Wahidyar. He is from Paktia province, and was therefore thought more likely to have to contacts with North Waziristan than Quetta.

However, Wahidyar's has said his contacts came from the south, according to Kate Clark from the Afghanistan Analysts Network who has been sifting through his account of the chain of events that let to the assassination. Four months ago, Wahidyar contacted an old friend from his mujadeen days, 'a trusted man among the Taleban' called Abdul Satar. Satar in turn nominated another man, Hamidullah Akhundza, the head of the state-run Ariana airline under the Taliban, as a go-between. Clark writes:

According to Wahidyar, in early September, Hamidullah indicated that the Quetta Shura wanted to start direct negotiations with the Afghan government and that it would probably be another go-between who would come to Kabul with a message from the shura. This turned out to be a man called Mullah Esmatullah who would kill Rabbani and leave Wahidyar and Stanekzai wounded.

Wahidyar felt comfortable with these contacts as he had fought with Hamidullah and Satar in the same mujahedin faction, the Harakat-i-Inqilab-i-Islami. But because both men came from the south, from Helmand and Kandahar respectively, Wahidyar did not have the same feel about who they really were. Hamidullah had spent time in Guantanamo, and so too, Clark believes, had Satar.

If anything, then, the trail leads south towards Quetta, and the failure of the Quetta Shura to denounce the killing also raises the question of whether some or all the leadership had a role in ordering the hit. However, the provisional assessment that the Haqqanis were involved could be based on secret evidence perhaps gleaned from interrogations of Esmatullah's driver and the companion he arrived with at the meeting with Rabbani.

There may also be an element of wishful thinking at play. If the Quetta Shura and Mullah Omar ordered or agreed to the assassination it would be a clear sign they have no real interest in peace talks and that the contacts so far with American officials have been a ploy.

Reflecting those fears, expectations of the Bonn conference on Afghanistan in December, are already being ratcheted down. Western officials now talk about to review development plans and renew international commitment to the country's future at Bonn. They no longer mention progress on reconciliation, which had originally been conceived as the third pillar of the conference.

Hopes that the Taliban would open a political office in Qatar are also fading. That plan had become bogged down anyway by Taliban insistence that it should be a quasi-embassy, a non-starter for Kabul and its western backers.

A definitive statement from the Taliban distancing itself from the Rabbani assassination would go a long way to lightening the gloom, but with every passing day, any such denial would be less convincing.