Counter-terrorism experts around the world are looking at the possibility that there was a kind of collusion between a violent, fanatical, splinter group of Eta and extremists from outside. There have previously been connections between Eta and the GIA, and Algerian terrorist group. But normally al-Qaeda would not work with non-Muslims, as they do not trust them. But al-Qaeda is not a fixed organisation, it is a shadowy phenomenon, and it is possible that there are people sympathetic to them, who have worked with them. Al-Qaeda also has form in Spain. They held their final eleventh-hour terror summit in northern Spain in July 2001, where Mohammed Atta, the main September 11th hijacker, briefed the others and sent news to Afghanistan about the imminent attacks.

What are the experts and governments saying about who was responsible?

The UK government is saying officially that it takes its lead from the Spanish investigation, but I can say that privately officials are holding their breath, hoping this is not al-Qaeda. If this is a Spanish issue, dreadful as that may be, at least it would be contained there. In the UK, the Joint Terrorism Analysis Centre inside MI5 is taking in all the input so far. It will be compiled into a report for the Joint Intelligence Committee and will be passed to the prime minister and parts of government.

What points to al-Qaeda?

The Spanish government is keeping an open mind and since the investigation is only just underway, that is probably the best thing to do. There is an analysis going on into the authenticity of the claim sent last night to a London newspaper office, claiming that the attacks were the work of al-Qaeda. There are several factors that point to them. Firstly there is the discovery of a van containing bomb detonators and Koranic chants. The second is the claim of responsibility from an obscure group in Canada, but we can perhaps dismiss that, but the most important is the claim sent to London saying that they did it. The fact that there were no warnings and that the attacks were so well synchronised also indicates al-Qaeda could have been involved.