Religion and the census

In response to a written question from Mike Weatherley (Hove, Conservative), Nick Hurd relayed a letter from Stephen Penneck, Director General for the ONS, dated 22 March 2011:

A question on religion was included in the Census in England and Wales for the first time in 2001 following the Census (Amendment) Act 2000. Responses to the question helped provide information which supplemented the output from the ethnicity question by identifying ethnic minority sub-groups, particularly those originating from the Indian sub-continent, in terms of their religion. The wording and design of the question and response categories were determined after extensive consultation with users and other key stakeholders and a programme of question testing.

But why should the government care?

Information from the religion question is used to supplement ethnicity data to gain a general understanding of society; to inform service provision and resource allocations; and for fulfilling legal obligations to monitor inequalities.

This isn't the sort of motive a libertarian can condone.