Are there really only around 3,000 Muslims in the town?
There are only 3 mosques, which may well be catering for say Sunni and Shia, and perhaps Bangla v Pakistani.
I worked on the 2001 census, and one thing very evident, was a great reluctance of some ethnic communities to get involved, however when the reasons were explained, and how the data collected would be used to everybody's benefit, then it was usually OK.
Nevertheless the feedback from 2001 showed that there might be about 1 mill people in the UK, living outside the mainstream bureaucracy.
I would like to think that the 2021 census, if it happens, would show a majority for no religion.