David Cameron's deep anxiety over Algeria
The decision not to come to Amsterdam was taken just before 6pm on Thursday, after the prime minister had spoken again to the Algerian prime minister.
You saw in his face, you heard in his voice, you could tell from the words just how anxious they are in Whitehall about further casualties.
I am being told that they are prepared for what are being called multiple casualties. Early on in this siege there was talk, all of it unconfirmed, of as many as 35 dead from all nationalities.
Now, when I put that to people in Whitehall expecting them to dismiss it as nonsense they said "we simply don't know the answer to this, but it may not be as wrong as you originally thought".
There are some British hostages that are now known to be safe, but I am told that up to 20 are still to be identified - some may still be missing, some could still be hiding, others could be injured and not be properly identified, but sadly, too, there may be others who are dead.
I am told that when the news came from the Algerian government that they had begun a military operation without notifying or consulting with other Western countries, including the UK, the reaction in the room - I'm told from someone who heard - was: "Please God, what are they doing?"
The reason for that I'm told was that the British government has offered the Algerian government advice on how to deal with a siege situation, either negotiations or a military solution.
Because the feeling in London, and I am told in other capitals too, was the Algerian government did not have the expertise to deal with this.
Now clearly they may well argue when this all becomes clearer that they had no choice that the militants involved, the Jihadists, were trying to move people off the base and that's why military action was taken.
Those questions, some of the answers we may get in a statement in the House of Commons in the morning, but tonight along with all those families who are anxious, inside Whitehall, inside Downing Street, there is real deep concern.