Buckingham Palace, October 30: “The Custodian of the Two Holy Mosques King Abdullah Bin Abdul Aziz Al Saud of Saudi Arabia today commenced a State Visit in London to the Queen and the Duke of Edinburgh.”

The Queen did more than just roll out the red carpet for King Abdullah: as well as the 21-gun-salute, the Household Cavalry and the rest, she invited two dozen of his family to stay at the Palace and another hundred or so to a lavish banquet. But these princes were merely a fraction of the Saudi entourage, which required five 747’s, a vast fleet of limousines and several of the most expensive hotels in London. Needless to say, not one member of this airborne caravan was a woman.

Britons do not begrudge King Abdullah his conspicuous display of oil wealth. It is not his court but his discourtesy that has caused offence. The Saudi monarch insists that he warned the British of the Al Qaeda attacks on London in July 2005, but that his warnings were ignored. This claim was investigated by a Parliamentary committee and found to be untrue.

What is true, though, is that the Saudi regime continues to promote Wahhabi Islam in Britain with vast sums of money. And there is plenty of evidence of links between Saudi-based Islamic “charities” and Islamist terrorism. But Britain’s restrictive libel laws inhibit open discussion of this sinister diversion of funds.

“Alms for Jihad,” an important study of such links by two distinguished American scholars, J. Millard Burr and Robert O. Collins, was withdrawn from publication by Cambridge University Press after litigation by a rich Saudi, Sheikh Khalid bin Mahfouz. Not only have all copies been pulped, but libraries have been obliged to return the book, which can only circulate unofficially in photocopied form.

According to my samizdat copy of “Alms for Jihad,” the Saudi monarchs support some 210 Islamic centres, 1,500 mosques, 202 colleges and almost 2,000 schools in non-Islamic countries. A significant proportion of these Saudi-funded institutions are in Britain.

On Tuesday, the day of King Abdullah’s arrival, the Times of London devoted its entire front page to a story based on another book, “The Hijacking of British Islam,” which revealed the violent ideas being propagated at many of the leading British mosques. An academic expert on Islam at Newcastle University, Denis MacEoin, and his researchers visited more than a hundred mosques over the past year, where they found a total of 80 extremist books and pamphlets openly on sale. Some are in Arabic or Urdu, but about half are in English — easily accessible to the police, who appear to have turned a blind eye.

One of these books, “Fatwa Islamiyah,” teaches that Muslims who convert to other faiths should be beheaded and that adulterers should be stoned. Another, “Women Who Deserve to Go to Hell,” is a misogynist rant against women who adopt western habits. Such literature, Dr. MacEoin says, inculcates “abhorrence” for anybody deemed to be “un-Islamic” — Muslims as well as non-Muslims. Both books were found at the most prestigious mosque in London, the London Central Mosque in Regent’s Park, which is funded by King Abdullah. Its director is a Saudi diplomat.

Dr. MacEoin blames the radicalization of British Muslims largely on the Saudi regime, which he finds has exercised a “powerful and malign” influence on Islam in Britain. It remains to be seen if King Abdullah or one of his minions will now try to have this book, too, suppressed. Its publisher is Policy Exchange, a conservative think tank with a more robust attitude to Saudi intimidation than Cambridge University Press.

In a free country, censorship is always problematic. As the Muslim Council of Britain official Inayat Bunglawala says, apparently without irony, “We live in an open, democratic society where it is not illegal to sell books which contain anti-Western views.”

But even democracies expect reciprocity. King Abdullah and his predecessors have suppressed religious freedom in Saudi Arabia for centuries. As “Custodian of the Two Holy Mosques” at Mecca and Medina, he refuses to permit a single church or synagogue throughout his kingdom — an area the size of Western Europe. He even declined to follow the example of other visiting heads of state in Britain, of laying a wreath on the tomb of the Unknown Soldier in Westminster Abbey — setting foot inside a church would apparently be “un-Islamic.”

The Saudis have their defenders. One of the wisest commentators on the Muslim world, Amir Taheri, writes in the London Times that the regime is slowly reforming itself. Women can’t drive in Saudi Arabia, but they make up over half of all university students and their share of its wealth is higher than in much of Europe. It is true that we need Saudi support in the war on terror. Saudi forces have, Mr. Taheri estimates, killed or captured about 800 Al Qaeda terrorists. We also still need Saudi oil.

But the Saudis need the West even more. King Abdullah may call himself Custodian of the Two Holy Mosques, but President Bush and Queen Elizabeth II are, in effect, custodians of the Custodian. The West must use its power as custodians, and as customers, to ensure that the hundreds of billions that we pay for their oil is not used to promote jihad in our midst.