An Islamic organisation in Wales has said that some Muslims in Cardiff are fearful of filling in their census forms.
Saleem Kidwai, head of the Muslim Council for Wales, believes up to 20,000 Muslims living in Cardiff didn't state their religion in 2001.
However, the last census suggested there were 11,000 people in Cardiff who described themselves as Muslim.
Kidwai said:
"People were apprehensive about filling in the forms, particularly the religious section of it, not knowing for what purpose the information would be used."
"It is vitally important that they tick that box because only then will we know the number of Muslims in this country and accordingly, the resources are allocated."
Each household in the UK is required to fill in the purple form, based on their circumstances on 27 March 2011.
Kidwai said the Muslim Council for Wales have been making a real effort to encourage more of the community to fill out the form accurately.
"In certain parts of the community they find it very difficult to fill in the forms, either for linguistic reasons or because of a fear of the forms.
"From a government point of view it is important that they can see what communities there are, what their requirements are and it's the same for us."
He added that accurate figures were important in understanding the 'strengths of the community' and to determine the areas which require further resources.
Cardiff council suggested the city may have lost out on up to £50m due to errors in the 2001 census and Cardiff's population figures have been fluctuation ever since.
This year's census will be provided in Welsh and English only – with guidance notes on how to fill out the form in 56 languages – up from 30 languages available for the 2001 census.
Cardiff council has guidance on how to fill out the census here.
Daniel Hewitt and Paul Heaney are trainee broadcast journalism students at Cardiff University. They also run the Politics Wales blog here.
