When historians of a future era look back on the Blair years, they will surely turn to two defining, contrasting images: a Prime Minister jigging and giggling with joy after securing the Olympic Games, and the same man, just a few hours later, with a face of thunder, vowing to hunt down terrorists and defend British civilisation.

For months Tony Blair has plotted and fretted over his legacy, only to have his historical inheritance set in stone in one tumultuous 24-hour period.

In between the euphoria and the carnage, Blair flew back and forth to Scotland; chaired the emergency Cobra Cabinet security meeting; opened, interrupted, and closed the G8 summit; and uttered three separate, intensely memorable statements on the terrorist outrage. Those words, and the accompanying iconic images, will form his political epitaph, for better or worse.

Blair is a master of rhetoric: he can deploy words to dissemble and demean, but he can also use them to articulate the feelings, fears and hopes of his listeners. He did this over the death of Diana, Princess of Wales, and he did it even more dramatically on Thursday, offering a resonant response to terrorism even before the scale of the devastation was known.

In his odd combination of Churchillian timbre and slangy idiom, Mr Blair framed the attacks and the necessary response as a Manichean struggle between civilisation and barbarity that would end in triumph over terror. Roy Jenkins wrote of Winston Churchill’s oratory that it produced “a euphoria of irrational belief in ultimate victory”. This was precisely the effect achieved by Mr Blair with a few short sentences written on the back of an envelope.

The impact was heightened by the entirely rational euphoria that preceded it. Aides said that they had never seen Mr Blair’s trademark smile wider than when he heard of Britain’s successful bid for the Olympics. On receiving the news by telephone, he performed a small dance of victory on the lawn at Gleneagles.

Here are the adjectives uttered by Mr Blair in his first, brief interview after the news: fantastic, extraordinary, momentous, magnificent, tremendous, amazing, brilliant, awesome, brilliant, and fantastic. This was Mr Blair as wild enthusiast, celebrating an astonishing political coup with a torrent of superlatives.

He bounded out of the hotel the next morning, a man all but airborne on his own success: Jacques Chirac humiliated, the Olympics secured, hosting a summit of the world’s wealthiest nations, with the glow of Live8 behind him. All was for the best in the best of all possible worlds. Then the first bomb went off. Unlike George W. Bush, photographed with his face in a rictus of shock as he learnt about 9/11, the cameras did not witness Mr Blair’s personal pathos, his transition from delight to horror. The full extent of the atrocity emerged slowly, and by the time he took to the podium any surprise had already worn off, replaced by a grim defiance.

The first statement was terse, tense and to the point, but it also established the themes that would recur through the coming hours. Twice he referred to the barbarity of the terrorists. “Whatever they do, it is our determination that they will never succeed in destroying what we hold dear in this country and in other civilised nations”: a way of life against a way of death. The Prime Minister’s hands shook as he spoke, his face was drained of colour. No doubt these were phrases that have been rehearsed often, in the dread certainty that they would be deployed eventually, but he gave every impression of spontaneity.

Returning to London from Scotland by helicopter, Blair had a chance to refine his thoughts. The resulting speech, delivered from Downing Street, was far more emotional and overtly patriotic, a speech more of sentiment than substance, precisely fulfilling William Hazlitt’s definition of powerful oratory: “Not to inform, but to rouse the mind.”

At times it was almost colloquial, delivered in the blunt language of the pub. “I think we all know what they are trying to do: they are trying to use the slaughter of innocent people to cow us and frighten us out of the things that we are trying to do, trying to stop us going about our business as normal, as we are entitled to do.”

But then came the echo of Churchill, the rise-and-fall cadence of the battle hymn. “We shall prevail . . . When they seek to change our country or our way of life by these methods, we will not be changed . . . When they try to divide our people or weaken our resolve, we will not be divided and our resolve will hold firm.”

The word oratory is associated with prayer, and Mr Blair’s summation at the end of the summit was more an invocation of belief than a statement of political resolve. The agreements made at Gleneagles, he said, marked “a beginning, not an end. And none of it today will match the same ghastly impact of terror. But it has a pride and a hope and humanity at its heart that can lift the shadow of terrorism and light the way to a better future.”

Barbarity and civilisation; darkness and light; black and white. “We speak today in the shadow of terrorism, but it will not obscure what we came here to achieve,” he said. “The purpose of terrorism is . . . to put all conventional politics in darkness.”

It seems hard to believe that only a few weeks ago some members of Mr Blair’s party were calling for his resignation. Yesterday even the Daily Express was commending his steely resolve. If this week’s attacks turn out to be the start of a sustained campaign, then that could change quickly, for although the shadow of Gordon Brown has temporarily receded again, that of the Iraq war continues to loom darkly.

Yet this may be stated in black and white: when future generations are taught about the political career of Tony Blair, the opening lesson will focus on a single week in July. A week that started with a pop concert, saw a surprise sporting success and a strange international summit, and ended in an act of mass murder that changed Britain for ever.

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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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