Foreign funding for extremism in Britain primarily comes from Saudi Arabia, but the UK government should set up a public inquiry into all Gulf funding sources, a report has said.

The report by the Henry Jackson Society also calls for the government to consider requiring UK religious institutions, including mosques, to be required to reveal sources of overseas funding.

The findings come as Theresa May faces pressure to publish the government’s own report into foreign funding of terrorism. The Home Office-led report was completed six months ago, and No 10 says ministers are still deciding whether to publish. MPs nervous of upsetting strategic relations in the Gulf have also decided not to publish a separate Foreign Office strategy paper on the region.

Saudi Arabia is likely to be angered by the findings since its dispute with Qatar has largely been based on the accusation that its Gulf rival is both the primary funder terrorism overseas and harbours terrorists that support the Muslim Brotherhood or Hamas.

The report claims: “Saudi Arabia has, since the 1960s, sponsored a multimillion-dollar effort to export Wahhabi Islam across the Islamic world, including to Muslim communities in the west.

“In the UK, this funding has primarily taken the form of endowments to mosques and Islamic educational institutions, which have in turn played host to extremist preachers and the distribution of extremist literature. Influence has also been exerted through the training of British Muslim religious leaders in Saudi Arabia, as well as the use of Saudi textbooks in a number of the UK’s independent Islamic schools.”

It adds: “A number of Britain’s most serious Islamist hate preachers sit within the Salafi-Wahhabi ideology and are linked to extremism sponsored from overseas, either by having studied in Saudi Arabia as part of scholarship programmes, or by having been provided with extreme literature and material within the UK itself.”

Apart from an official public inquiry into the funding of terrorism, the report calls for the government’s planned new commission for countering extremism announced in the Queen’s speech to address the financing of extremism from overseas a matter of priority

Tom Wilson, a fellow at the Centre for the Response to Radicalisation and Terrorism at the society – and author of the report, said: “While countries from across the Gulf and Iran have been guilty of advancing extremism, Saudi Arabia is undoubtedly at the top of the list.

“Research indicates that some Saudi individuals and foundations have been heavily involved in exporting an illiberal, bigoted Wahhabi ideology. So it is ironic, to say the least, that Saudi Arabia is singling out Qatar for links to extremism when it has patently failed to get its own house in order.”

The report argues that although Saudi leaders have acknowledged the need to rein in some of the funding of extremism, including by setting up a counter extremism centre this year, the level of funding of Wahhabism has been on the increase.

It claims in 2007 Saudi Arabia was estimated to be spending at least $2bn (£1.5bn) annually on promoting Wahhabism worldwide. By 2015 that figure was believed to have doubled.

The impact of this increased spending may well have been felt in Britain: in 2007, estimates put the number of mosques in Britain adhering to Salafism and Wahhabism at 68. Seven years later, the number of British mosques identified with Wahhabism had risen to 110.

It argues that Saudi Islamic charitable groups have tended to fund Wahhabist ideology. Some of Britain’s most prominent extremist preachers — such as Abu Qatada, Abu Hamza, Abdullah al Faisal and Shiekh Omar Bakri — have all sat within what can be described as a broadly Wahhabi/Salafi ideology, the report says. In 2014, it was estimated that Britain’s Salafi Mosques had a collective capacity for a 44,994-strong membership.

The report by no means exclusively blames Saudi – pointing out that the Qatari-funded Al-Muntada Trust has been connected with a number of mosques where radicalisation has taken place. Specifically, in the case of a group of young British men from Cardiff, it has been suggested that “attendance at the al-Muntada-linked Al-Manar Mosque was significant in their radicalisation and decision to travel to Syria and join the Islamic State”.

In Austria foreign funding of mosques has been banned, while in France a temporary ban was imposed. Measures have also been considered in Germany, in the wake of a leaked intelligence report highlighting foreign funding of mosques by endowments close to the governments.

The report concludes: “The attempt by several states to influence Islamic communities and advance an illiberal – and at times anti-western – version of the Islamic religion appears to have been an intentional and systematic policy, with the level of funding allocated to this effort believed to have grown in recent years.

“While some of this financing appears to originate from private individuals and independent foundations, research by the German intelligence agencies and others has pointed to these foundations being closely linked to governments of several Gulf states.”