At Roy Jenkins’s memorial service in Westminster Abbey yesterday, shafts of sunlight streamed over the heads of a congregation containing pretty well every surviving political figure from the second half of the 20th century. Three former prime ministers shared the front pew of the quire. The only notable absentee, the man who was supposed to give the address, was Tony Blair, the adopted political son of Lord Jenkins of Hillhead.

In normal circumstances, the current Prime Minister would not have dreamt of missing such an event. He was fond of Jenkins, and saw him as his mentor, his father figure. It was therefore particularly poignant that a council of war — that most adult of tasks — had drawn Mr Blair to Washington.

For the Prime Minister, in the past few months, has grown up immeasurably. He seems to have undergone the transformation that many men, particularly oldest sons, experience when their father dies. John Mortimer describes the process in Clinging to the Wreckage: “Sudden freedom, growing up, the end of dependence, the step into the sunlight where no one’s taller than you and you’re in no one’s shadow.”

When Mr Blair won power, he seemed like a boy pretending to be a man. He had no experience of even the lowest rung of ministerial office. It didn’t help that the youngest premier for more than a century looked even younger than he was.

As experience has taken the place of innocence, a new Blair has emerged. Approaching 50, and with two election victories to his name, he has cast off the insecurities of youth. Responsibility for war has turned him into a sombre but secure adult. Many traits that characterised his first term are evaporating.

He no longer seems to feel the need to trim. Recklessness rather than caution is the immediate danger. Instead of meeting his critics halfway, these days he simply reasserts his position with greater conviction. At Tuesday’s No 10 press conference, he surprised journalists by answering pretty well every question forthrightly and with aplomb.

Nor does the Prime Minister crave the reassurance of public acclaim. In his first term, he used popularity to insulate him like a security blanket. He checked his policies with focus groups before embarking on change, and shied away from those that did not play well. Now he has proved himself willing to take an unpopular stance and turn it, by force of conviction, into a popular one. Opinion polls on the war and his leadership have moved dramatically in his favour.

If Mr Blair has grown up, what might he do with his new-found maturity? He will unleash it on President Chirac, for a start. M Chirac has, until recently, been able to exploit the British PM’s rather starry-eyed, youthful idealism about Europe to extract concessions that were not always in Britain’s interest in areas such as the common foreign and security policy. After the war, the French may find Mr Blair rather harder to roll over. On Tuesday, he warned “old” Europe that it faced a “reckoning” over its relations with America; talk which would have been unimaginable a year ago.

Instead of acting like the “adaptive child”, who seeks to please and hides his anger, Mr Blair has grown into an adult prepared to say what he thinks and do what he likes. French presidents always act like that, perhaps because they tend to assume office at a much greater age. At last our Prime Minister may prove their match.

The other man who is feeling the force of Mr Blair’s new-found assurance is Gordon Brown. The Chancellor used to rely on his ability to squish his kid brother, the Prime Minister. He dominated Mr Blair intellectually and played psychological games with him, such as avoiding meetings or refusing to tell him the contents of his Budgets until the last minute. This dynamic is changing. When the Prime Minister wanted to fix a meeting with the Chancellor some weeks ago, Mr Brown tried to make him come to the Treasury (where the Chancellor sits on a chair much higher than that of his guest, who is immediately cast in the role of supplicant). “No, you come over here,” barked Mr Blair down the phone. “I’m the f***ing Prime Minister!”

Insouciance about others’ opinions helps politicians to achieve more. Churchill did not win the war by worrying what other people thought. Margaret Thatcher would not have tamed the trade unions had she listened to her critics.

But her example illustrates the danger too: that Mr Blair, like her, will cease so completely to care what people think that he will lose touch with his Cabinet, his party and the country. Jenkins, that great biographer of prime ministers, would have been the man to judge whether this phase for Mr Blair marks the end of the beginning or the beginning of the end.

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