Specific evidence was 'too sensitive' to be released

Downing Street admitted yesterday that its dossier of evidence linking Osama bin Laden to the terrorist attacks in America was "not complete" and would not convict him in a court of law.

But government officials insisted there was a "smoking gun" proving his guilt which could not be included in the 21-page dossier published yesterday because it would reveal the methods or sources used by the security services. "There is evidence of a very specific nature relating to the guilt of bin Laden and his associates that is too sensitive to release," the document said.

The crucial undisclosed piece of evidence has been shown by the Prime Minister to Charles Kennedy, leader of the Liberal Democrats, and Iain Duncan Smith, the Tory leader, who was said to be "100 per cent convinced by it". The Prime Minister may also outline the evidence to other world leaders as he seeks to maintain the international coalition against terrorism.

The dossier published yesterday was based on material collected by American agencies, including the CIA and FBI, as well as the British intelligence services.

The US agencies cleared the use of their information before publication and the document was discussed closely with the Bush administration before it was issued.

The US is still considering whether to publish a similar report and further evidence may be made public by the British Government.

Jack Straw, the Foreign Secretary, predicted the dossier would help to convince people with questions in their mind about the culpability not only of Mr bin Laden but also the whole of his al-Qa'ida organisation. He said "an enormous amount" of the evidence was based on intelligence. "You can't publish raw intelligence without very seriously putting at risk the human sources from which it comes or the overall security arrangements and intelligence arrangements we have in place," he said.

The dossier relies heavily on circumstantial evidence about the previous atrocities carried out by Mr bin Laden and al-Qa'ida and the similarities between these acts and the atrocities on 11 September – meticulous long-term planning, a desire to inflict mass casualties, suicide bombers and multiple simultaneous attacks without warnings being issued.

But Tony Blair's official spokesman insisted the report included important evidence, citing the claim that the detailed planning for the attacks was carried out by one of Mr bin Laden's close associates. There was also evidence that he indicated shortly before 11 September that he was about to launch a major attack on America and that his close associates were told to return to Afghanistan from other parts of the world by 10 September.

The dossier said at least three of the 19 hijackers involved in hijacking the four planes on 11 September have been positively identified as associates of al-Qa'ida.

But Number 10 refused to name them.

Asked if the evidence was mainly circumstantial, a Downing Street spokesman replied: "It would have been perfectly possible to have released absolutely nothing and for us to have made the case as we have done against bin Laden and al-Qa'ida. This is an exceptional situation, therefore it is exceptional that we are publishing this document.

"We are being as open as we can while taking every measure we can to protect intelligence sources and gathering."