King Abdullah will go home to Saudi Arabia today with the charges of human rights protestors ringing irritatingly in his ears. But his controversial visit may well have left an unpleasant legacy for the people of the country which has feted him with full state honours.

There was a hint of it in a report written this week by Dr Denis MacEoin, an Islamic studies expert at Newcastle who previously taught at the University of Fez. Leading a team of researchers over a two-year project, he uncovered a hoard of malignant literature inside as many as a quarter of Britain's mosques. All of it had been published and distributed by agencies linked to the government of King Abdullah.

Among the more choice recommendations in leaflets, DVDs and journals were statements that homosexuals should be burnt, stoned or thrown from mountains or tall buildings (and then stoned where they fell just to be on the safe side). Those who changed their religion or committed adultery should experience a similar fate.

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Almost half of the literature was written in English, suggesting it is targeted at younger British Muslims who do not speak Arabic or Urdu. The material, which was openly available in many of the mosques, including the East London Mosque in Whitechapel, which has been visited by Prince Charles, also encourages British Muslims to segregate themselves from non-Muslims.

There is, of course, nothing new in such reports. Investigative journalists have over the years uncovered all manner of material emanating from Muslim extremists in various parts of Britain. Earlier this year an undercover reporter for Channel 4 filmed preachers and obtained DVDs and books inside mosques which were filled with hate-filled invective against Christians and Jews. They condemned democracy and called for jihad. They presented women as intellectually congenitally deficient and in need of beating when they transgressed Islamic dress codes. They said that children over the age of 10 should be hit if they did not pray. Again the main mosque chosen for exposure was influenced and funded from Saudi Arabia.

And on it goes. A few years earlier one Sheikh Abdullah el-Faisal, a Jamaican convert who had studied at a Saudi university, was caught spouting about how "Jews are rotten to the core and sexually perverted, creating intrigue and confusion to keep their enemies weak". Later jailed for nine years for urging his audience to kill Jews, Hindus and Americans, he was recorded as saying: "You can use chemical weapons to exterminate the unbelievers. Is that clear? If you have cockroaches in your house, you spray them with chemicals." Among his followers was Germaine Lindsay, one of the 7/7 bombers who killed 52 people and injured 700 others on the London transport system in 2005.

Small wonder, then, that Abdal Hakim Murad, the student chaplain at Cambridge University pronounced in the Channel 4 film: "I regard what the Saudis are doing in the ghettoes of British Islam as potentially lethal for the future of the community."

Muslims have always responded that such individuals constitute a tiny and highly unrepresentative minority of their community in Britain. But concerns are growing within Muslim circles about the increased reach of Wahhabism, Saudi's obscurantist and intolerant form of Islam in which Osama Bin Laden has his roots. There are fears for the increasingly baleful influence it may be having on young British Muslims.

Yahya Birt, an academic who is director of The City Circle, a networking body of young Muslim professionals, estimates "Saudi spending on religious causes abroad as between $2bn [£960m] and $3bn per year since 1975 (comparing favourably with what was the annual Soviet propaganda budget of $1bn), which has been spent on 1,500 mosques, 210 Islamic centres and dozens of Muslim academies and schools".

More than that they have flooded the Islamic book market with cheap well-produced Wahhabi literature whose print runs, Birt says, "can be five to 10 times that of any other British-based sectarian publication, aggressively targeted for a global English-speaking audience." This has had the effect of forcing non-Wahhabi publishers across the Muslim world to close. It has put out of business smaller bookshops catering for a more mainstream Muslim market.

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The Saudis have also reserved for foreigners 85 per cent of the places at the Islamic University of Medina, which boasts of having more than 5,000 students from 139 countries. Despite the fact that British students gained the reputation in Medina of being unreliable, lazy, and prone to dropping-out, there have so far been hundreds of British graduates who have returned to the UK espousing the rigid Saudi worldview.

The strategy has in one way backfired on the Saudis. They accelerated their aggressive missionary work – targeting China and Russia as well as the UK – in reaction to the activities of Iran in the 1980s which, after its theocratic revolution, was pumping out propaganda across the globe. The Saudis had already been pump-priming Islamic terrorists to fight the Soviets in Afghanistan, at the behest of the Americans and funding among other things the schools in Pakistan that gave rise to the radicalism of the Taliban.

But the Saudis lost control of this new global Wahhabism. During the First Gulf War in 1991 there were splits among Wahhabis, both in Saudi Arabia and outside, over whether it was right to allow infidel American troops to protect the land of Islam's two holiest shrines, at Mecca and Medina. Anti-Saudi Wahhabis, such as the infamous hook-handed cleric Abu Hamza in Britain pronounced that the Saudi king had broken his divine covenant with God. It was therefore the duty of scholars to charge him with unbelief and incite the masses to rise against him in rebellion. Groups such as the radical Hizb ut-Tahrir capitalised on an anti-Saudi sentiment which spread throughout the Wahhabi community.

The focus of violent Islamic radicalism has shifted from Wahhabis in Saudi to anti-Saudi Wahabis in Iraq and other conflict zones where jihadists have learnt the heady lesson that if you are brutal and narrow-minded enough you can defeat the most powerful army the world has ever seen.

Since 9/11 the Saudis have begun to row back on their funding of fundamentalism abroad, according to Mehmood Naqshbandi, the Muslim advisor to the City of London police. Too late. The damage has been done.

The Saudis do not call themselves Wahhabis. That is largely a derogatory term applied by their opponents. Many Saudi religious leaders insist on calling themselves just Muslims, extending the implication that Muslims who do not share their particular interpretation of Islam are not proper Muslims at all. But some Saudis describe themselves as salafis. And it is salafism that has taken root among many second- and third-generation British Muslims.

To understand why you need to know a bit of theology. Salaf is the Arabic word for a pious ancestor. It refers to the generation of Muslims who personally knew the Prophet Muhammad, and those who knew that generation. Muslims regard any religious figure in the first three generations of Islam as a salaf. The term was first used in the 20th century by reformers in Egypt. But it has now been appropriated by the Wahhabists.

"Not all Muslims approve," says Dr Philip Lewis, who is the Bishop of Bradford's adviser on Islam. "Some say that the Wahhabi have hijacked a very venerable term for a very reactionary agenda to give them a bogus respectability."

Salafism comes from a way of looking at Muslim texts which date back to no later than that third generation after Mohamed. It disregards the four main traditions of Islamic law and practice which developed over the centuries since then. Rather like the Protestant reformers in Christianity it speaks of going back to the roots. Abdal Hakim Murad, who lectures in Islamic Studies at Cambridge explains: "Just as the Protestants wanted to get rid of the saints and shrines, the Aristotle and Aquinas of medieval theology, so the salafis declare as 'unbelief' most of the practices which are normative to Islam in the Indian subcontinent." Salafism is known for its scriptural rigidity, intense literalism, deep intolerance and rejection of traditional Muslim scholarship.

So why is this attractive to modern British Muslims? Because they are searching for an identity but rejecting the factional ethnic Indian subcontinental politics of their parents, says Mehmood Naqshbandi, the author of the City of London's guide to Islam for non-Muslims. "They are having an identity crisis." They have no patience with the old tribal rivalries of their parents' generation. They have weak links with the Indian subcontinent. They are unhappy with rural imams imported from Pakistan who do not understand the culture of sex, drugs, rock'*'roll, and politics that surrounds them. And they have been educated in a system that trains them to challenge and to research on their own.

"They are ripe for salafism, which claims to have the most transparent route back to the sources of the Prophet's time. And salafism's antagonism to mainstream orthodoxy makes it attractive to youth," he adds. They need not bother with the long tradition of Islam. The 7/7 suicide bombers Mohammed Siddique Khan and Shehzad Tanweer were salafis. So was the "shoe bomber" Richard Reid. From there they provided easy prey to the al-Qa'ida notion that anyone who isn't a salafi is the enemy.

Hostile commentators such as Stephen Schwartz, author of The Two Faces of Islam, dismiss salafism as a mere synonym for Wahhabism. It is cover, he says, just as in a previous age "euro-communist" became a palatable euphemism for Stalinist. Abdal Hakim Murad disagrees. "No one in the Muslim world denies that the theology preferred by terrorists is salafi/Wahhabi," he says. "But if most terrorists are salafis, most salafis are not terrorists. After the Iranian revolution the safe generalisation was the Shia were more dangerous [than the Sunni] because they had a martyrdom complex. You don't hear that said much today."

Naqshbandi agrees. "There's nothing in salafi principles which implies any relationship with political violence, it is just that if you are inclined that way salafism is a very attractive wrapper for you."

Some extremists have tried to take advantage of this by targeting salafi mosques in an attempt to recruit young Britons for violent jihad. They have adopted similar entryist tactics to those once employed by Militant in the Labour Party. Abu Hamza succeeded at Finsbury Park mosque, but a two-year infiltration plot at Brixton mosque, where the shoe-bomber Richard Reid worshipped, failed because non-violent salafis were alert to the danger.

The first individuals to report violent salafis to the British police were the non-violent salafis, who greatly outnumber the extremists, but the police largely ignored them. After 9/11 the leaders of several salafi mosques realised the danger of their position. "They recognised that they had become a useful vehicle for extremists and the problem of antagonism [this caused] between them and the rest of the Muslim community," says Mehmood Naqshbandi, " and they have gone to great pains to work with the authorities at all levels."

One conservative salafi leader went so far in an internet question session to tell Muslims that it was OK for them to work with the intelligence services to uncover violent jihadists. They had a duty to protect Britain, he said, which is a good place to be a Muslim. After 9/11 salafis in Birmingham subsidised the translation and distribution of a celebrated 1998 fatwa by Ibn Baz, the Saudi Grand Mufti, condemning terrorism, hijacking and suicide bombing.

Police are watchful but not unduly alarmed. Of the 1,526 mosques in Britain only 68 are salafi, according to Naqshbandi, and many of these are very small breakaways from bigger local mosques who refuse to take the salafi line. One Special Branch officer says privately that police have developed strong contacts inside salafi groups.

There is also an understanding that the non-violent salafi are their best allies against the jihadists. "They can pull people out of violence more easily than outsiders," said a member the Special Branch counter-terrorism unit. "They are the people they're going to listen to because they speak the same language. The closer you are theologically to the real hardliners the greater the chance you have of influencing them."

The problem is that terrorism needs only a tiny number of adepts to be devastatingly effective. And the fear is that the Saudis have created an ideological framework which makes that more possible. One mainstream Deobandi teacher told Yahya Birt that the salafi influence had bred such a climate of suspicion among his pupils that, even when teaching classic traditional texts, he had to leave out everything that could not be traced explicitly back to the Qur'an and the accepted sayings of The Prophet, the hadith. "British Islam has become more purely scripturalist," says Birt, "and petrodollar Wahhabism has been a key agent of this change."

It has also, says Abdal Hakim Murad, "made the public style of discourse and preaching more confrontational. . . . Salafis anathematise their opponents and their opponents internalise the violence of that language. It has soured the atmosphere considerably."

New technologies of mass communication have added to the problem. With the internet, videos and tapes ordinary Muslims are now studying texts once reserved for scholars in the higher reaches of clerical training. The result is a new highly individualistic theology which often reads holy texts in a literalist way with no understanding of the contexts in which different parts of the Islamic scriptures were framed.

It all facilitates interaction between young Muslims from Britain, Pakistan and the Arab world. But that is as true in an al-Qa'ida training camp in Afghanistan as it is on the internet.

"Violence is not inevitable," says Philip Lewis, "but it creates the environment in which it is possible for that to be the next step". Abdal Hakim Murad agrees. "Salafism increases the likelihood of combustion but doesn't mean it's inevitable. Wahhabism is Islam's unstable isotope, it regularly produces detonations around the edges," he says. "If you throw into the crucible racism, social exclusion and the other experiences of being a young Muslim in Britain's inner cities, and then combine that with British foreign policy blunders overseas, and then add that to a theology that divides the world in a Manichean way into good and evil, us and them, then – if you put all that together – you may have a very explosive mixture."

It is to be hoped, therefore, that when King Abdullah comes to leave for home today the Queen and British Prime Minister remember to say thank you.

Wahhabism: a history

By Michael Savage

Wahhabism is a conservative movement within the Sunni denomination of Islam which was founded by an 18th-century cleric, Mohamed ibn Abdul Wahhab.

The founder's intention was to return Islam to its early roots by stripping it of what he regarded as the alien influences added by the generations of Muslims since the death of Mohamed in 632.

Wahhab's principles were drawn mainly from direct readings of the Koran, and the life of Mohamed. He was also influenced by the writing of an earlier Sunni scholar, Taqi ad-Din Ahmad ibn Taymiyyah, who shared a belief that Islamic practice needed to return to a "purer" interpretation of the religion's fundamental texts.

According to Ibn Abdul Wahhab, all the ideas that had been added to Islamic worship after the "Salafis" – the three generations which followed the death of the prophet Mohamed – were false and divergent from true Islam.

He is believed to have been motivated by what he saw as a decline in standards in the Arab world and a regression back into polytheism, which had been present in the Arab world before the development of Islam.

In particular, Ibn Abdul Wahhab criticised idolatry in the form of saint worship and shrine visitation. He also believed that each Muslim had an individual responsibility to learn and adhere to the commands in the Koran and the speeches of the prophet. He was prepared to be very critical of fellow Muslims whom he regarded as having developed "false practices", even going as far as to declaring jihad on those who engaged in the kinds of Islamic worship of which he disapproved.

The term "Wahhabi" was first used pejoratively by the opponents of Ibn Abdul Wahhab to describe both him and his followers. In 1924, Wahhabist fighters conquered what is now the western part of Saudi Arabia. It has been the dominant strand of Islam in Saudi Arabia since the kingdom was unified in 1932, and its growth overseas has in part been helped by wealth accrued from the country's oil reserves.

Today, Wahhabism is present in Muslim communities across the West. It is also a strong strain of Islam in Arab states such as Kuwait and Qatar, and has some followers in Somalia and Palestine.