In the war on terror, like every other war, there are two theaters: the battle front and the home front. The outcome may be decided in either one.

On the two main battle fronts in Iraq and Afghanistan, the issue hangs in the balance. Al Qaeda’s capture of three American soldiers in Iraq has diverted attention from the unspectacular but substantial success of General Petraeus’s surge. It is a similar story in Afghanistan, where the major success of the coalition forces in killing the Taliban commander Mullah Dadullah has been eclipsed by instability in neighboring Pakistan.

As important as what happens on the ground is the way it is reported back home. Mark Urban, the B.B.C. defense correspondent, spent several days with a U.S. infantry unit in one of the most dangerous outskirts of Baghdad. His fair, balanced and dramatic reports, aired this week at length on prime-time TV, were rare exceptions to the usual anti-American and anti-war bias of the B.B.C.

The American soldiers came across as likeable, perceptive, normal young men who, despite having just lost two men, did not fit the B.B.C.’s standard GI image of trigger-happy, blinkered rednecks. They had faith in their commanders and their mission. In their eyes, a precipitate withdrawal would nullify the sacrifice made by their dead comrades. The message is: give the surge time to succeed, and this war can be won.

Back in Washington, however, British correspondents never let a day pass without insisting that the anti-war Democrats, not George W. Bush, now represent the American people, while assuring us that Republican rats are deserting the President’s sinking ship. On the home front, the B.B.C. tells us, public opinion has lost faith in the commanders and the mission. The message is: regardless of what happens in Iraq, the war is lost.

Here in Britain, there is the same gulf between what happens on the front line and what people believe back home. The predicted eruption of violence in the southern provinces where British troops are being replaced by the Iraqi army has not occurred. None of the commanders in Basra wants to rush this process.. They know that talk of a premature pull-out is encouraging the terrorists, the militias and their Iranian backers.

Yet defeatists are drowning out calmer voices in Parliament, encouraged by Tony Blair’s imminent departure and the possibility that his successor, Gordon Brown, can be persuaded to cut his losses and run. So far, Mr. Brown has kept his counsel. However, just as the Democrats are putting Republican presidential hopefuls under pressure to repudiate Mr. Bush, so the British Tories may put Mr. Brown under pressure to repudiate Mr. Blair.

The Left has always been soft on war and terror, but the British public is now getting used to anti-war speeches from the Right. The Conservative leader, David Cameron, has already distanced himself from the Bush administration, even though he voted for the war. We shall shortly discover the full extent of his opportunism.

Last week I happened to see Mr. Cameron at a memorial service for the journalist Frank Johnson, one of whose famously witty columns he read before a congregation that included most of London’s media establishment. “Very prime ministerial,” I heard someone say as Mr. Cameron processed out of the church. In the modern media lexicon, to be “prime ministerial” (or “presidential”) has nothing to do with gravitas and everything to do with youthful enthusiasm. Barack Obama is a perfect example.

Mr. Cameron likes to keep up his profile by stunts designed to prove that he is in touch. Last week he went to stay for a couple of days with a Muslim family in Birmingham. Afterwards, he posted the following comment on his website: “Every time the B.B.C. or a politician talks about ‘Islamist terrorists’ they are doing immense harm (and yes I am sure I have done this too, despite trying hard to get this right.) Think of Northern Ireland – ‘IRA terrorist’ was fine because it marked them out as part of a terrorist group, ‘Catholic terrorists’ would have been a disaster. Yet that is the equivalent of what we are doing now.”

He doesn’t get it, does he? When Catholics talk about martyrs, they mean those who die for their faith. When Islamists talk about martyrs, they mean those who kill for their faith.

Islam is the religion founded by Mohammed. Islamism is the ideology of Muslims who wish to impose their religion, including its political and legal system, on non-Muslims, if necessary by jihad. That is what many of the most powerful clerics in the Islamic world advocate. It is what global organizations such as the Muslim Brotherhood and Hizb ut Tahrir put into practice by radicalising the young. It is what produces an unlimited supply of terrorists for al Qaeda, the Taliban and Hamas.

Mr. Cameron’s refusal to mention Islamism in the same breath as the war on terror is like refusing to mention Nazism or Communism in connection with the Second World War or the Cold War. Not all Muslims become Islamists, just as not all Islamists become terrorists, but these are three concentric circles. We can’t win the battle of ideas if we don’t even know what we are up against, let alone how to grasp the variable geometry of jihad.