In terms of the significance of Cobra being called, I think it is a very clear indication that officials believe this now to be without doubt a terrorist incident. What we are told by Government sources is that one of the men shouted "Allahu Akbar".
Clearly that kind of information filtering back makes the Government very, very nervous indeed. We know from many previous reports, and the many court cases we have had, that the idea of harming a soldier has been a repeated facet of terrorist plans in the past.
I think the Government will want to ask itself some very critical questions about whether this is a small group of people acting alone, or whether indeed they are part of a bigger plot. That will be their immediate concern.
David Cameron is in Paris, in discussion with Francois Hollande - clearly that will be put to one side. He is listening in on the Cobra briefing that's taking place. After that we expect him to come out and give a press conference.
Quite honestly, I would be extremely surprised if he didnt immediately get on the plane home. Parliament is not sitting at the moment. But I would be surprised, given the severity and the seriousness of the incident, if it wasn't recalled pretty soon too.