LONDON – London’s longest day began like any other: overcast. I was on the Tube, just after 9 a.m., when it hit me: that sickening feeling of dread that only terrorist attacks engender. The announcement that the entire London subway system was suspended could mean only one thing. The full horror emerged only gradually, but from that moment it was clear that Al Qaeda’s fingerprints were all over the capital.

I was swept up in a human wave as Earl’s Court station was evacuated, and snatches of conversation overheard suggested to me that others had jumped to the same conclusion. Though nobody yet knew that bombs had just exploded at three other Tube stations, one had an inkling that one had just had a lucky escape.

Outside, the rain was falling gently across the capital, but not enough to wash the blood from the streets. I thought I would be safer on a bus, but I was wrong. A couple of miles away, in Bloomsbury, a double-decker bus had been ripped apart, perhaps by a suicide bomber. The first of many?

There was no panic, no hysteria, no melodrama. Londoners had been expecting something like this at least since September 11, 2001, and memories of Irish Republican terrorism from the 1970s through the 1990s are still fresh. I still recall hearing a thump in the night, thinking that a child had fallen out of bed, and discovering that it was an IRA bomb in the neighborhood.

Word spread quickly, but the reaction was slower to take shape. When it came, it was exactly what you would expect from the nation that endured the Blitz: grim determination to defy this new onslaught. If the Nazis could not crush London’s spirit, neither would the Islamists.

Until the attack, London had been enjoying its best week for 60 years. By coincidence, this week London is commemorating the end of the Second World War. Last weekend we had witnessed the extraordinary spectacle of Live 8, when a quarter of a million people converged on Hyde Park to hear what seemed like all the greatest rock stars alive. (At least, I think they were alive.) Then had come the unexpected bonus of the Olympics, the announcement of which left Londoners feeling unsure whether to laugh or cry.

Well, now we know. There will be no celebrations now, no more euphoria, no more self-satisfaction. Instead, London has suffered a hideous reality check.

The British are at their best in adversity. We shall bury our dead without pomp, but with dignity. Blessed are those who mourn, for they shall be comforted. But London, our poor, beloved London, the city where my children and I were born, is not blessed today, but bloodied. While politicians and police chiefs spoke to cameras, in the background the great bell of Westminster Abbey tolled for the dead.

My first thought was for my four children, scattered across three West London schools. Struggling past the screaming sirens of police and ambulances, with helicopters overhead, through crowds of bewildered commuters, I arrived at my 13-year-old daughter’s school in Hammersmith.

The principal was calm and sensible amid the chaos. I could take Edith home if I liked, but would I please not panic the other girls. When Edith emerged from her classroom, Dr. Carpenter explained to her that the terrorists intended to disrupt normal life, and that she would not stand for it. Despite the parents, who were phoning frantically and turning up unannounced, normal service would resume as soon as possible. For five years, Prime Minister Blair entrusted his only daughter to Dr. Carpenter’s care, and yesterday I understood why.

By this time it was clear that buses, too, were being attacked and hence unsafe. So we walked the mile or two home. At noon, Mr. Blair appeared on TV to address the nation. He looked grave, resolute, and very, very angry. We have seen the prime minister in tough situations before, but never had he looked like this. His wrath against what he called a barbaric assault on civilized nations was genuine, and exactly what we wanted to hear.

However, one could also detect in his tone that the casualties must be much more serious than had been admitted officially. By noon it was clear that dozens of people at least must have died, as hundreds of the injured arrived in hospitals. As the hours ticked by, the death toll rose, as the emergency services slowly brought out the victims.

London’s Underground railroad is the oldest in the world, and its tunnels are the deepest. It was always known that if terrorists attacked the Tube, the rescue operation would be a nightmare, and so it has proved. At King’s Cross, the Piccadilly Line is hundreds of feet underground. There it took hours for the medical teams to get people out, and at least 21 died in the inferno.

In my family, as in countless others, there was a sense of gratitude to God for our deliverance. Once all four children were safely gathered in, we prayed together for those less fortunate than ourselves.

There is no feeling in London, as there was in Madrid last year, that we are being punished for our participation in the Iraq war, still less that the Americans or Israelis are somehow to blame for our misfortune. In France, an emergency meeting of security ministers was summoned immediately: The French know that, despite their hostility to the Atlantic powers and their appeasement of America’s enemies, Paris could well be next.

The G8 summit at Gleneagles, Scotland, was the occasion for the attack, but Mr. Blair judged the mood correctly when he refused to call the whole thing off. He made the point forcefully that the world’s leaders were there to alleviate poverty, and that the terrorists had deliberately disrupted their efforts. Wisely, he made a quick trip down to London to assess the situation firsthand, but returned the same evening to Gleneagles.

Comparisons of human catastrophes are always invidious, and it would be wrong to claim that yesterday’s ordeal has anything like the historic significance of September 11, 2001. But though London’s 7/7 was incomparably less devastating than New York’s 9/11,it was in some ways just as sinister. The threat was invisible: It did not descend from the sky, but oozed up from the subterranean depths.

The ingenuity of evil men is infinite, and the terrorists have done real damage, not only to life but also to the infrastructure. It will be weeks before London’s transport system recovers from this attack.

Yet there is a silver lining. The fact that Al Qaeda did not even attempt to hijack airplanes this time demonstrates that airport security really has improved and is now sufficient to deter terrorists.

Mr. Blair will have to think again about the bill now passing through Parliament which outlaws incitement to religious hatred – an iniquitous measure twice rejected before, whose sole purpose is to appease Britain’s 3 million Muslims. It cannot be right, now that jihad has wrought havoc in the heart of London, that the media should be prevented from identifying and criticizing those who are dedicated to destroy the West. Under the new law, for example, the Muslim Council wants journalists to replace the phrase “Islamic terrorist” with “international terrorist.” Self-censorship will be the inevitable result.

The relationship between the Muslim minority and the rest of the population is bound to alter as a result of yesterday’s terrible events. To restore trust will not be easy, especially if it emerges that native Britons as well as foreign terrorists were responsible. True, there was swift condemnation of terrorism from the Muslim community. My friend Sir Iqbal Sacranie, the leading Muslim moderate, urged Muslims to help the police to catch the “murderers.” But even he seemed more concerned about possible Islamophobia than he was about the attack itself. No doubt he and other Muslims are ashamed of those who kill in the name of Islam. But as long as jihad is preached from the pulpits of many mosques as the duty of every Muslim, the horrors of 9/11 and 7/7 are doomed to be repeated ad infinitum.