Both areas have large and growing populations of Pakistani origin who originally came over to work in the textile mills of Bradford, Dewsbury, Oldham and Blackburn.

Latest census figures show that the ethnic minority population of Bradford grew from 17 per cent to 22 per cent between 1991 and 2001; Leeds from 7 to 8 per cent; Oldham from 9 to 14 per cent and Kirklees, including Dewsbury, from 11 to 14 per cent.

The race riots in Oldham, Burnley and Bradford in 2001 were a visible sign that fear and ignorance still permeated these communities. It was an atmosphere ripe for exploitation by extremists such as the British National Party, whose leader, Nick Griffin, unsuccessfully challenged Ann Cryer, the Labour MP in Keighley, West Yorkshire, at the last general election. The riots produced two huge reports, which were a devastating indictment of years of effort — and not a little wishful thinking in Whitehall and Westminster — about how integration was proceeding.

The conclusions by Ted Cantle, who led the investigation, made troubling reading for Whitehall. After visiting the riot towns and other multicultural cities, he admitted that he was shocked by the “depth of polarisation”.

He found communities whose lives “often do not seem to touch at any point, let alone overlap and promote meaningful interchange”. The white and ethnic minority communites were effectively living “parallel lives”.

This retreat behind ethnic lines was also documented by a separate independent inquiry into Bradford. The inquiry by Lord Ouseley, the former chairman of the Commission for Racial Equality (CRE), discovered a city fragmenting along ethnic, religious and cultural lines. Schools were places of “virtual apartheid” where racial conflict, harassment and “Islamophobia” thrive.

Communities had little, if anything, to do with people outside their race or religion. White people believed that there was favouritism towards the ethnic minorities and a “white flight” of the middle class had left an “underclass” of poor whites. At the same time Muslims said that they were the victims of prejudice.

Last night the chairman of the CRE said that Muslim leaders must bend over backwards to reassure the public that there was no place in their community or faith for suicide bombers.

Trevor Phillips said that he recognised how hateful it was for Muslim leaders to have their motives doubted, but in the current atmosphere of anxiety and fear they must speak out often. A Muslim MP said that the community had not done enough to tackle extremism. Shahid Malik, the Labour MP for Dewsbury, said: “We have to look within the community. There is extremism there. We have not done enough to actually deal with that.”

Mr Phillips said that members of his staff had been sent out into the communities in West Yorkshire to tell people that division between communities and rising fear was exactly what the London bombers intended to cause. “They want everybody to be afraid of each other,” he told The Times.

Mr Phillips said: “I know how difficult and how hateful it is for Muslim leaders to have their motives doubted, but they need to understand that they have to bend over backwards to reassure people. That is their part of the bargain.

“The part of the bargain for people like me and the police is to stop opportunistic and idiotic people turning on Asians and Muslims who really have nothing to do with this.”

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