I am on the Prime Minister's plane, studying Tony Blair's face at the end of a 9,000-mile odyssey that has taken us through five cities, crossing and then recrossing the Atlantic, for 43 hours of non-stop, sleep-defying, time-zone-hopping diplomacy.

The Prime Minister has lost weight in the past two weeks. He has the wide eyed, somewhat startled look of someone running on adrenaline.

His is the face of a man who feels the burden (and the spotlight) of history upon him. The shoulders are a little more hunched; the face seems sharper; the nose, in profile, more angular. There is something newly hawkish about this face.

And as he swooped from one destination to the next -consoling grieving families in New York, standing alongside President Bush in Washington to declare war on Osama bin Laden, and working to reinforce an anti-terrorism consensus in Brussels -the language of war grew ever graver.

Blair casts himself as EU president candidate

Speaking on French TV, Tony Blair sang the praises of the EU and sketched his agenda for its future, all in fluent French

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Blair's diplomatic marathon was, in some ways, a bizarre one: over-ambitious, not without posturing, marked by moments of high farce as well as high emotion. But when the history of this conflict is written, the strange zig-zagging flight of the British Prime Minister will be recalled as a pivotal event.

September 20, Heathrow:

A greasy dawn is breaking somewhere on the edges of Heathrow airport, and the posse of bleary political reporters accompanying Mr Blair has assembled in the gloom, outside the gate to the VIP entrance.

Outside, because the gate is barred, the guards are nowhere, and we are facing the first of what will be a litany of delays caused by excessive (and frighteningly inefficient) additional security measures in a world in which the commercial airliner had suddenly become an instrument of terror.

Charles de Gaulle Airport:

We are on the state-of-the-art British Airways Boeing 777 Mr Blair has chartered for the trip, and the Prime Minister has come aboard, after his meeting with President Chirac of France.

There is a strange, jangling tension aboard Flight 9129, partly because of the momentousness of the event we are witnessing, but also partly, for most of us, because this is the first time we have flown in a plane since September 11.

The humour is brittle and strained, a long way from the joshing, ironic atmosphere of the campaign trail, the last time I was aboard a plane with the Prime Minister. A brief flutter of excitement wings around the cabin, as it is reported that in his departing remarks, Mr Blair spoke of conflict within "days". There is a dash for the onboard telephones, only three of which work at the same time.

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