To be a tourist in your own back yard is a disorienting experience. Showing a teenage American cousin around London this week, I have been obliged to see through her eyes the city in which, exactly half a century ago, I was born, and in which I have lived for most of my adult life.

I thought I knew London pretty well. But when we trooped off to Buckingham Palace to watch the changing of the guard, I realized that I had no idea what to expect. I never found out, because the ceremony was cancelled. Why? “Due to the inclement weather,” said one of the police officers herding the crowds — as if, given the vagaries of the insular climate, a drizzle of rain in mid-August were some kind of surprise.

So we walked to Westminster Abbey, where it cost over $50 to be allowed through the door of what is still supposedly a place of worship. The staff hurried us past the monuments: when I stopped briefly to explain something to my cousin and my daughter, one of the staffers told me curtly that I was “causing a blockage” — as if the place were an intestine, rather than Edward the Confessor’s great monastic foundation, where the English crown their monarchs and honor their dead.

Later we stopped at a bank, Coutts in the Strand, so that our guest could change some dollars. The cashier asked her “whether she had just come in off the street.” Just because the Queen banks there, the staff seems to think they can treat ordinary customers with disdain, despite the fact that, with the City of London decimated by the credit crunch, even royal bankers could do with the business. So London is not as enjoyable an experience for tourists as it should be. Even Britons can be made to feel like strangers in their own land.

When we took our American cousin to an Indian meal at a long-established restaurant, we were shocked to find ourselves treated as second-class citizens: after a long wait, we were given the worst table, and the service was slow and offhand. Then we realized why our custom was so little valued: the Muslim customers were seated at the best tables, while dhimmi (non-Muslims) were relegated to a back room. The waiters had all come from Pakistan — recently, to judge from their English — and if they had been educated at all, it would probably have been in a fundamentalist madrassah. Their attitude implied that they had heard nothing good about the West.

All over the country, mosques are springing up like mushrooms. Some of them merely serve the fast-growing Muslim population, but many offer a pulpit to Islamist preachers. The trouble is that non-Muslims are not usually welcome to come and listen, and so it is hard to know which mosques are potential sources of trouble.

A few months ago, many people were alerted to this problem by the TV program “Undercover Mosque,” in which reporters for the documentary series “Dispatches” secretly filmed radical preachers. Broadcast at prime time on the Channel Four network, the film painted an alarming picture of the jihadi sermons that imams have been preaching in some of the most important mosques in Britain. This column quoted some of the incendiary material at the time.

Following the broadcast, the West Midlands police force asked the program makers of “Dispatches” to let them see the footage to determine whether or not the material amounted to incitement to commit acts of terrorism.

But the police investigation of the jihadist preachers quickly turned into a kind of inquisition directed against the program makers. The case was passed to the Crown Prosecution Service, which made extraordinary allegations against the “Dispatches” team. The editors of the documentary were accused of distorting the sermons by taking short extracts out of context.

Channel Four, the most liberal of the major network broadcasters, was threatened with prosecution for hate speech — an especially damaging allegation for this corporation, which (like the BBC) is publicly owned but (unlike the BBC) funds itself commercially.

In the end, the prosecution did not go ahead, but not before the networks and press had been thoroughly intimidated. It would be a brave press executive who would dare to send undercover reporters into the mosques now.

At least the pre-emptive cringe, to which I referred in last week’s column, has not gone quite as far in Britain as in Holland, where the Catholic Bishop of Breda, Martinus Muskens, has just invited Christians to address God as “Allah” for the sake of “harmonious living.” “Allah is a very beautiful word for God,” Mr. Muskens told viewers on Dutch TV. “Shouldn’t we all say that from now on we will call God ‘Allah’?”

Well, we might as well turn Westminster Abbey into a mosque. The abbey is, of course, a stone’s throw from the Houses of Parliament — as neat a juxtaposition of the two main components of Western civilization, Judeo-Christian, and liberal democratic, as you will find anywhere. Defenses against the threat of Islamist terrorism are being strengthened all over Westminster and Whitehall. But the cultural threat — what Pope Benedict XVI’s secretary, Monsignor Georg Gänswein, recently called “the Islamization of Europe” — is ignored. Once the churches and synagogues of Europe are Islamized, the parliaments and courts will follow suit.