Brian Jones: Were terrorists really planning a dirty bomb?

It transpires that this exotic sounding material had not actually been obtained

After more than 15 years in chemical warfare intelligence, I cannot recall hearing about osmium tetroxide until this week.

After more than 15 years in chemical warfare intelligence, I cannot recall hearing about osmium tetroxide until this week. I spent countless days discussing potential chemical warfare agents with experts from Porton Down and across the world. We considered at length the agents and the precursor chemicals which could be used to make them for inclusion in the export control lists designed to defeat WMD proliferators and terrorists. There were numerous chemical compounds of concern, but osmium tetroxide was not among them.

Suddenly we are told that the security services have foiled a fiendish plot by international terrorists to detonate a dangerous chemical weapon based on this compound in London. In some way the signals intelligence collectors at GCHQ in Cheltenham, their US counterparts at the National Security Agency (NSA), MI5 and the police are all involved. There were telephone intercepts within this country and to Pakistan. A link with al-Qa'ida is implied, but not explicit. The term "dirty bomb" is used.

However, as the story unfolds, expert chemists and toxicologists tell us that this unusual chemical is not "controlled." It can be bought on the internet in glass containers. Although it is hazardous there are other chemicals in industrial, medical and academic use that are both more readily available and potentially more dangerous. It seems just as likely that osmium tetroxide would be added to conventional explosives to promote a bigger bang.

It is not clear whether the targets mentioned - the London Underground, Gatwick or Heathrow airports and perhaps a shopping centre within the M25 - were discussed by the terrorists or are the speculation of the security officials involved. It then transpires that this exotic sounding material had not actually been obtained by the putative terrorists, nor is there any indication that arrests have been made. How then has the "terror gas attack" been foiled?

It all begins to sound like so much froth. But it may be dangerous froth. It has never been sensible to discuss so openly the source of intelligence information. With the amount of publicity about mobile phone communications over the last few years, it is surprising that anyone is unaware of their vulnerability to interception. And if the authorities really believe that osmium tetroxide is a chemical we should be worried about, why on earth are they advertising it on every media outlet in the western world and beyond? As a "red herring" it may mislead the terrorists, but it will also confuse many of those charged with guarding our security and managing the consequences of an attack.

At first, it crosses my mind that this information could have entered the public domain as the result of an ill-conceived attempt to boost the reputation of one or other of the hard-pressed intelligence and security agencies. Much criticised in the wake of the Iraq war for the absence of WMD, and increasingly pressed by the Treasury to justify their funding, there is already evidence of a propaganda offensive with "leaks" at the early stages of the Butler review.

But then, with Mr Blunkett's statement on Wednesday, I wonder whether our new knowledge of osmium tetroxide was inspired by the Home Office to support their policy initiatives. Alternatively, he may simply be seizing an opportunity. Either way, the intervention does not inspire confidence that the terrorist threat is being properly addressed.

The discovery of a plot to detonate a "dirty bomb" laced with poisonous chemicals is said by the Home Secretary to justify tough measures to combat terrorism. The term "dirty bomb" is most often associated with radiological weapons and creates a vague connection with a nuclear attack. The clever use of language invites the mind to an interpretation beyond the words used. But if he thinks that such a bomb would be the stuff of Armageddon to which the Prime Minister recently referred, he is quite wrong. It would not be much, if at all, beyond the conventional attacks with which the IRA made us all too familiar in recent decades.

Although I believe Mr Blair was a little hysterical in invoking Armageddon, he is, unfortunately, absolutely right to raise the spectre of real chemical or biological warfare agents in the hands of Osama bin Laden's terrorists. We know that those closer to the core of his organisation have made progress towards acquiring capabilities that could dwarf the Madrid bombings, an "osmium tetroxide bomb" or even the 11 September attack on the World Trade Center in New York.

Whatever the background to this particular episode, I find it frightening that those who are leading our defence against terrorism either do not properly understand the requirement or are prepared to see the public misled as a short term expedient to achieve policy goals, however necessary.

The Leader of the Opposition has expressed concern about uncertainty over who is in charge of counter-terrorism. I think there is much greater concern that those who claim to be in charge do not, apparently, have a clue about the problem.

The writer was head of the branch of Defence Intelligence Staff responsible for the analysis of intelligence on nuclear, biological and chemical warfare