Some British Muslims live such segregated lives they believe the UK is a Muslim nation and 75 per cent of the population follow the Islamic faith, a government report will reveal this week.

The major review by Dame Louise Casey, the government’s community cohesion Tsar, will expose how some communities have created a parallel existence with their own separate housing estates, schools, and television channels.

The report will “send shock waves through the system”, a Whitehall source told The Times, adding: “It’s going to be quite hard reading for some people.”

In northern cities such as Bradford, Dewsbury and Blackburn, some Muslims will almost never leave their isolated areas and interact with mainstream British society, the document explains.

The Savile Town area of Dewsbury, for example, is 98.7 per cent South Asian, and has been described as “the most segregated area in the UK.” The majority of the population follows the ‘fundamentalist’ Deobandiand school of Islam.

“Certain Muslims, because they are in these communities and go to Muslim schools, think Britain is a Muslim country. They think 75 per cent of the country is Muslim”, a source who has seen the report told the paper.

The government does not have any serious integration strategy to manage the effects of mass migration, and the report is expected to attack the Home Office’s inaction on the matter and the now prime minister Theresa May’s record as Home Secretary.

Dame Mary previously investigated failings by children’s services at Rotherham council after the Muslim rape gang scandal, and those familiar with her latest report described it as “full-fat Louise”. She has reportedly been forced to see off attempts by the Home Office to water the document down.

The cohesion Tsar has also examined the social alienation felt by some white working class people in her work. However, the report will stress that the ‘far right’ poses a less significant threat that Islamist terror.

The report will also explain how the government has not done enough to defend Prevent, the counter-extremism policy, against misinformation put out by Islamist and far-left groups, who claim the work to tackle radicalization is “discriminatory” and even racist.

The National Union of Students (NUS), for example, has been working with Islamist sympathisers to call for students to “resist” Prevent for some time, holding events teaching them about “resisting the impact of the Prevent duty” and “organising non-compliance”.