A new report is calling on the government to investigate Saudi Arabia's funding of Islamic extremism in the UK.
The foreign affairs think tank Henry Jackson Society (HJS) said there was growing evidence of Gulf countries (primarily Saudi Arabia) as well as Iran providing funds to mosques and Islamic educational institutions in the UK that have hosted extremist preachers and have been linked to the spread of extremist material.
The organisation is now calling for a public inquiry into the role and influence of Gulf countries and Iran on UK-based Islamist extremists, the majority of whom, it said, "sit within the Salafi-Wahhabi ideology", which originated in Saudi Arabia.
"Since the 1960s, Saudi Arabia has sponsored a multimillion dollar effort to export Wahhabi Islam across the Islamic world, including to Muslim communities in the West," the report said.
The think thank also claimed there have been "numerous cases" of British individuals who joined extremist groups in Iraq and Syria who are thought to have been radicalised by "foreign funded institutions and preachers."
An investigation into a link between foreign funding and Islamic extremism in the UK was commissioned in 2015 by the then prime minister David Cameron, but it has not been published yet.
Earlier in July, the Guardian said the report had been given to Downing Street last year, but Prime Minister Theresa May is yet to decide whether to publish it or not, with some claiming the delay in making a decision might be influenced by close ties the UK has with Saudi Arabia.
Labour MP Dan Jarvis said the report shed light on "very worrying" links between Saudi Arabia and the funding of extremism. He called on the government to release its report.
"In the wake of the terrible and tragic terrorist attacks we have seen this year, it is vital that we use every tool at our disposal to protect our communities," he said, according to the BBC. "This includes identifying the networks that promote and support extremism and shutting down the financial networks that fund it."
The Saudi embassy in London said in a statement sent to IBTimes UK that the claims contained in the report were "baseless" and "categorically false". It added the Saudi Kingdom has been targeted by attacks at the hands of al-Qaeda and the Isis terror groups.
"The Kingdom of Saudi Arabia affirms, once again, that it has not and does not support or fund any group that has direct or indirect links to any terrorist organisation," read the statement, adding that the Kigndowm has been "at the forefront of fighting the spread of extremism and terrorism at home and abroad."
"All charitable donations to educational and religious establishments by the Saudi state are made to registered charities in the UK. Saudi charities are prohibited from transferring money abroad and cannot operate abroad except through the King Salman Humanitarian Aid and Relief Centre or the Saudi Red Crescent, which is a semi-government entity," the embassy said.
"Our long-standing relationship with the UK and work in countering such extremists has been successful. UK Prime Minister Theresa May, as well as the past Prime Ministers, have previously spoken of the strength of Britain's relationship with Saudi Arabia and how it has helped to keep people on the streets of Britain safe," it added.
"We do not and will not condone the actions or ideology of violent extremism and we will not rest until these deviants and their organisations are destroyed."
The Home Office has not responded to a request for a comment.
A government spokesman was quoted by the Telegraph as saying: "Defeating the evil ideology of Islamist extremism is one of the greatest challenges of our time. The Commission for Counter-Extremism, which the PM announced earlier this year, will have a key role to play in this fight.
"We are determined to cut off the funding which fuels the evils of extremism and terrorism, and will work closely with international partners to tackle this shared global threat, including at the upcoming G20 summit."
The report comes at a sensitive time as Saudi Arabia is among several Gulf states involved in a diplomatic row with Qatar, which has been isolated after being accused of sponsoring terrorism and adopting policies that can destabilise the area.
David Otto, a UK-based counter-terrorism expert, believes the HJS report is not surprising and there is "no doubt" of existing links between foreign funds and Islamic extremism in the UK. However, he believes only a cooperation between the UK and Gulf countries can tackle extremism.
"We must move a step beyond these state accusations - it only alienates these governments in favour of extremists propaganda - and focus on engaging with these governments and other key stakeholders, especially well respected Islamic scholars, to provide a contextual interpretation of the Quran and the Hadith, particularly those versions used by groups like ISIL , Boko Haram and AlQaeda," he said.
"The idea of accusing Gulf states of directly or indirectly supporting violent extremism is what groups like ISIL expect. Religion and politics are intertwined in Saudi Arabia and it will be a futile task to try and separate those two crucial elements. Saudi Arabia will not stop donations to Islamic religious charities or groups that show legitimate need on one hand and divert this resource to extremists promotion [on the other].
"An alternative ideological interpretation must come from Saudi Arabia and other gulf states working hand in glove. Without such intervention , their charity work will always be interpreted as support for extremism however hard they try to refute this claim."