Tony Blair’s decision to defer his holidays is a matter more of symbolism than substance. The Prime Minister is perfectly capable of making telephone calls from the beach but the picture of him there while conflict in Lebanon and Israel rages may not have been a comfortable one. Mr Blair is right to stay put until it becomes clear whether and when a UN resolution on this Middle East crisis is likely to be adopted.

There is, nonetheless, little chance of the politics of this region returning precisely to what Condoleezza Rice, the US Secretary of State, described as the “status quo ante”. There is, as Mr Blair put it in Los Angeles this week, an “arc of extremism” emerging across the Middle East. How to counter it and to promote, in the Prime Minister’s words, an alternative “arc of moderation” will be the principal question in foreign policy long after Mr Blair has disappeared from No 10. And, at first sight at least, it appears that the confrontation in and around Lebanon has reinforced and emboldened the leadership of the arc of extremism.

The divisions between fanatics of Sunni and Shia Islam seem to have been partially set aside in the present situation. While most outsiders might regard Hamas, Hezbollah or al-Qaeda as local variations on a similar theme, the truth is different. Al-Qaeda is a militantly Sunni sect dedicated to restoring the character and the boundaries of the Caliphate of 500 years ago. Hamas, although Sunni and dogmatic, has been shaped by the Israeli-Palestinian struggle and has a strong nationalist streak to it. Hezbollah, by contrast, is zealously Shia in the model of its major sponsor, Iran, and thus is heretical in the eyes of Sunni opinion.

This helps to explain why the original response of governments and religious leaders in Egypt, Jordan and, especially, Saudi Arabia to events in Lebanon was muted. There may be no love lost for Israel there, but the Jewish state does not represent the challenge to majority Islam that the Shia bid for political and spiritual leadership constitutes. Out on the Arab street, though, Hezbollah propaganda has been effective, with every misguided (in both senses of that term) Israeli bomb being exploited. Further death and damage of the type witnessed yesterday in Lebanon will surely boost Hezbollah and might derail the diplomatic initiative.

Shia and Sunni terrorist groups cannot, however, agree on a permanant alliance while their militias are slaughtering each other in parts of Iraq, notably in Baghdad. As the Shia-led coalition administration there assumes military control of further provinces, it will be harder for Sunnis to portray its members as allies of the United States rather than fellow Muslims. Hezbollah may be gaining a form of credit in Lebanon and beyond for being capable of firing hundreds of rockets at Israeli towns but the mercifully modest casualties it is inflicting suggest that it is far better at launching missiles than at targeting them accurately. In but a few weeks’ time, Hezbollah’s weaknesses may be apparent.

There is still a risk that the dictum of “my enemy’s enemy is my friend” may take hold, despite the well-established trend for conflict within radical Islam. If that “unity” takes root, the task of supporting moderates who have benefited from the splits in the extremist camps will become harder. What is truly a battle within Islam will be disguised as what it is not, a contest between all Muslims and the democracies. Mr Blair will have much to ponder when finally he begins his holiday.