http://news.bbc.co.uk/1/hi/uk/2711645.stm British officials have presented evidence which they claim shows that al-Qaeda has been trying to assemble radioactive material to build a so-called dirty bomb. They have shown the BBC previously undisclosed material backing up their claim. It includes secret intelligence from agents sent into al-Qaeda training camps in Afghanistan by Britain. Posing as recruits, they blended in and reported back. SAS officer inspects a deserted Afghan camp They revealed that Osama Bin Laden's weapons programme was further on than anyone thought. British officials said on Thursday Bin Laden now has the expertise and possibly the materials to build a crude radioactive bomb. The government says evidence suggests that by 1999, Bin Laden's priority was to develop a weapon of mass destruction. He had acquired radioactive isotopes from the Taleban to do this, officials said, adding that development work on the "dirty bomb" had been going on in a nuclear laboratory in the Afghan city of Herat. Evidence 'credible' The government even has al-Qaeda training manuals which detail how to use a dirty bomb to maximum effect. For a second opinion, the BBC showed some of the material to an expert on al-Qaeda. "I think this is genuine," said Dr Mustafa Alani, of the Royal United Service Institute. From nuclear weapons the threat is very, very slim Gary Samore "It is credible. This is proof that al-Qaeda put a lot of effort into collecting information and educating other members of the organisation. "It is possible to produce this sort of weapon." British military personnel worked with intelligence officers to gather material which was taken to Porton Down defence research centre in Wiltshire. Their conclusion was that al-Qaeda had a small dirty bomb but probably not a full blown nuclear device.