The terrorist attacks that have shaken Britain have now produced more disaster. That the man shot by police in Stockwell was not a bomber but an innocent victim is a tragedy. The friends and family of Jean Charles de Menezes are, understandably, devastated. The Brazilian Government has called for a full explanation, and that must be forthcoming. The Metropolitan Police were right to issue a statement swiftly, and right to express unconditional regret. But neither the police nor the public can recover from this setback until the circumstances have been examined. The inquiry by the Independent Police Complaints Commission, which begins today, should scrutinise any weakness in police procedure, question the operational guidance given to SO19, the special armed force trained by the SAS, and look again at the system of volunteer armed police.

Meanwhile, the reaction to Mr Menezes’s death has been commendably sensible. Most people understand the pressures on the police during what Sir Ian Blair, the Metropolitan Police Commissioner, has called its biggest operational challenge ever. They know that when dealing with potential suicide bombers normal procedures cannot apply. A false judgment or a delay of only seconds could lead to disaster. Britain is now facing a threat amenable neither to reason nor restraint. The shoot-to-kill policy, introduced by Lord Stevens, Sir Ian’s predecessor, is, sadly, inevitable. That fact is acknowledged by civil libertarians, moderate Muslim leaders and politicians alike.

The London Underground is a long way from the Egyptian resort of Sharm el-Sheikh. But the attacks on two hotels and a coffee shop there, killing at least 85 people, many of them Egyptians, show that for the perpetrators there is no distinction between them. Their targets are not just Westerners, but ordinary civilians, Christian or Muslim, whose crime is to represent the peaceful way of life anathema to the extremist adherents of an ideology based, as Tony Blair said, on a perversion of Islam.

The attacks in Egypt have nothing to do with the war in Iraq, which the Egyptian Government vigorously opposed, or with the Palestinian cause, which Cairo has peacefully tried to advance. They were carried out to further al-Qaeda’s obscurantist ideology, and no amount of Danegeld paid by politicians would buy off their bombs.

Egypt is no stranger to terrorism. Indeed, the assassination of President Sadat in 1981 can be seen as the birth of al-Qaeda: Ayman al-Zawahiri, Osama bin Laden’s operations planner, was jailed for his involvement. Since then extremist offshoots have carried out a series of attacks on ministers, civilians and tourists, including the 1997 massacre at the Temple of Queen Hatshepsut in Luxor. Cairo’s response has been unremitting: terrorists have been arrested, tried by military tribunals and hanged. Terrorism, however, feeds on misery and myth. The Egyptian crackdown has won al-Qaeda converts, just as the events in Iraq are now attracting those determined to exploit the violence as a means of destabilising the entire region. Iraq is not the cause of bombings in London; it is, undoubtedly, a factor in giving fanatics political cover and in providing a “rationale” for apologists.

Britain’s hunt for the bombers must not be compromised by the shooting at Stockwell. But neither must it become a myth of police brutality to recruit young men to extremism’s ranks.