An investigation into the foreign funding of jihadi groups in Britain said to focus mainly on the support provided by Saudi Arabia may never be published as the findings are “very sensitive”, the Home Office has admitted.

The inquiry was authorised in 2015 by former Prime Minister David Cameron in exchange for Liberal Democrat support for the extension of British airstrikes against Islamic State into Syria.

The Home Office’s extremism analysis unit had been directed by Downing Street to investigate foreign funding of extremist groups in the UK and for findings to be shown to then-Home Secretary Theresa May and Mr. Cameron.

However after 18 months, the Home Office has confirmed the incomplete report might not be published, calling the contents “very sensitive”, reports The Guardian.

A decision on the future of the investigation would be taken “after the election by the next government”, a Home Office spokesman said.

It is thought the report focused on Saudi Arabia, which ascribes to a hardline, Wahhabist branch of the Islamic faith.

European leaders and diplomats have condemned Saudi funding of Islamic extremism, including Norway’s former ambassador to Saudi Arabia, Carl Schiøtz Wibye, who said the Gulf kingdom has had “a tremendous influence on the spread of the Islamist ideology”.

German Vice Chancellor Sigmar Gabriel has also urged Saudi Arabia to stop supporting Islamists in Germany, saying: “Wahhabi mosques are financed all over the world by Saudi Arabia. In Germany, many dangerous Islamists come from these communities.”

Noted followers of Wahhabism include Lee Rigby murderer Michael Adebolajo, shoe bomber Richard Reid, 7/7 ringleader Mohammad Sidique Khan, and hate preacher Anjem Choudary.

UK Independence Party (UKIP) leader Paul Nuttall called for a ban on Saudi Arabia funding mosques after the Westminster terror attack, saying that “with Saudi funding of mosques comes radicalisation”.

“Maybe the government should look at the funding of mosques in this country because I don’t believe that Saudi Arabia should be funding mosques in this country particularly as it’s a country that spreads radicalisation,” he said.

Two weeks prior to the Bastille Day Nice attack in France, a Saudi-funded mosque opened in the city. The owner is the Saudi Arabian Minister for Islamic Affairs, Sheikh Saleh bin Abdul Aziz Al-Sheikh.

Saudi money also funded the Islamic Society of Boston mosque believed to have radicalised Boston Marathon bombers Tamerlan and Dzhokhar Tsarnaev.

Associate Director of The Henry Jackson Society Douglas Murray estimates there are “thousands” of Saudi-funded Wahhabi mosques across Europe, with the Saudis paying for the buildings and appointing clerics.

“In 2007 it was estimated that there were around 70 Wahhabi mosques in Britain. By 2015 the number had risen to 110,” with the amount of money flowing into these mosques at a “record high”, Mr. Murray wrote in a commentary for The Sun.

Saudi Arabia has also been influential in supporting some of Britain’s most prestigious universities, including Oxford University which received £2 million from Prince Sultan Salman bin Abdul Aziz al-Saud in 2005 and Cambridge University which received £8 million from Prince Alwaleed in 2008.

In April 2017, Prime Minister May visited Saudi Arabia and held talks with King Salman which focused on “bilateral relations and cooperation”.