Do we still need Tony Blair? The British prime minister’s position has never looked more precarious. He is beset by enemies from every side, and his own party seems to be deserting him. He is accused of selling peerages in exchange for secret loans. He has alienated many by his robust education policy and his prosecution of the war on terror. There is no end in sight in Iraq. The Economist magazine is calling on him to resign.

Does this mean that Mr. Blair is about to quit? We know only that he will go before the next election. In the fall of 2004, just after undergoing minor heart surgery, he revealed that he would not seek a fourth term in office. The next general election is expected in 2009, and the assumption has hitherto been that Mr. Blair will hand over to his anointed successor, Chancellor of the Exchequer Gordon Brown, no later than 2008. However, many Westminster insiders predict his resignation this year or next.

Yesterday, Mr. Blair sailed as usual through his weekly grilling at Prime Minister’s Questions. The leader of the opposition, David Cameron, did not lay a glove on him. Mr. Cameron dare not accuse Mr. Blair of corruption: His own party has a bad record and won’t reveal the names of its own donors. His own solution – state funding for political parties – is a ludicrous one for a man who calls himself a Conservative. He did cheekily ask the prime minister: “When’s he off?” Mr. Blair gave nothing away. He is clearly not ready to leave the stage just yet.

Why? Not because power corrupts, but because the exercise of power inculcates a sense of responsibility. While the media has been full of the cash-for-peerage scandal, the prime minister has been keeping his eye on the ball. The Islamist threat is growing, not diminishing, by the day.

This week, for example, the trial has opened at the Old Bailey, London, of seven British-born Islamists, mostly trained in Pakistan by Al Qaeda, all accused of plotting a bombing campaign designed to disrupt energy or water supplies or to blow up crowded London pubs or nightclubs. One of them allegedly tried to obtain a nuclear bomb from the Russian mafia via Belgium. Britain, according to another, “needed to be hit because of its support for the US.” The aim was to kill as many of their fellow Britons as possible. Two more members of the conspiracy are being held in Canada and New York. The latter, a Pakistani-born American by the name of Mohammed Babar, has pleaded guilty and will give evidence at the Old Bailey trial.

But convictions are notoriously difficult to secure in terrorist trials under the adversarial system of justice. The home secretary, Charles Clarke, now supports a shift to an inquisitorial system in terrorist cases, because it offers better protection to the public. In France, magistrates interrogate suspects before their lawyers are brought in. Nobody wants to give up the judicial system that has served the English-speaking peoples so well for more than a thousand years. But we have never faced such a menace before and we may have to make an exception for terrorism.

Then there is Iran. Despite mealy-mouthed statements by the foreign secretary, Jack Straw, to the effect that air strikes to stop Iran from acquiring nuclear weapons are “inconceivable”, a leaked letter revealed this week that Britain is secretly pressing for a U.N. resolution that would permit a military option. Meanwhile, more evidence is emerging that the Iranians will soon have nuclear missiles.

What is Tony Blair’s response? You would not know it from reading the British press, but on Tuesday he gave the first of three important speeches on how to defeat Islamist terrorism. The next will be delivered in Australia, and the last, in a fortnight’s time, in the US.

In this opening salvo, Mr. Blair had two main targets: the Islamists and their appeasers. He sees the war on terror as above all a battle of ideas: “This terrorism … will not be defeated until its ideas, the poison that warps the minds of its adherents, are confronted, head on, in their essence, at their core … Their attitude to America is absurd; their concept of governance pre-feudal; their positions on women and other faiths, reactionary and regressive.”

“The only way to win,” he declared,” is to recognize this phenomenon is a global ideology; to see all areas in which it operates as linked and to defeat it by values and ideas set in opposition to those of the terrorists.”

As for the appeasers: Mr. Blair contrasted his own “strongly activist” policy with “the doctrine of benign inactivity,” which remains “the majority view of a large part of Western opinion, certainly in Europe.” He denounced the “profoundly wrong” European habit of “pushing the responsibility onto America, deluding ourselves that this terrorism is an isolated series of … incidents.”

There is no other Western leader who is so persuasive in this battle of ideas. President Bush and the Australian prime minister, John Howard, are equally brave. Only Mr. Blair, however, has a chance of influencing the other Europeans. With friends as unpopular in Europe as the president, the prime minister hardly needs enemies. Yet, as the Bush administration has belatedly realized, the US needs European support if it is to defeat Al Qaeda, stop the Iranians in their tracks, and finish the job in Iraq.

So: Do we still need Tony Blair? I fear that we do. You only have to listen to his likely successor to see why. It was Gordon Brown’s big day yesterday: He gave the Budget speech, one of the great parliamentary occasions of the year. He pressed all the right buttons to curry favor with his party. Britain’s tax burden may be about to overtake Germany’s, but there was plenty of money for Labor’s favorite causes.

Yet he hardly mentioned terrorism, except to announce a memorial for its victims. He claimed to have doubled the homeland security budget since September 11, and promised a little more money for the armed forces in Iraq and Afghanistan. But he did not mention Iran, let alone Islam. Mr. Brown is a Scottish socialist who likes to vacation on Cape Cod but despises “swivel-eyed” American neocons. I suspect that includes Mr. Bush and most of his administration.

Of the three men who dominate the British scene, Mr. Brown is, and I fear always will be, just another politician. Mr. Cameron is still a politician too, though a young one who will grow in stature. Only Tony Blair, however, has shown himself a statesman.