Did the 2001 Census overstate the number of Christians and understate the number of non-religious?

The 2001 Census asked the question 'What is your religion?":-

2001 Census Question on Religion

Office of National Statistics results of What is your religion question:

As the BHA says:-

 'What is your religion?', the question in the 2001 census used in England and Wales gave a far higher figure for ‘Christian’ than all other surveys. The 'Christian' box was selected by 71.74% of respondents in England and 71.90% in Wales.

The Scottish figure, where respondents were asked about the religion they were brought up in, as well as their current religion, showed significantly fewer respondents ticking 'Christian': 65.08%, in spite of far higher figures for Church attendance in Scotland.

The corresponding figures for ‘None’ were: England 14.6%, Wales 18.63% and Scotland 27.55%. A closed question which assumed that respondents would have a religion undoubtedly inflated the number of respondents ticking a religious box and reduced the number of those ticking 'none'.

The figures were probably also distorted by the fact that the question appeared immediately after a series of questions on ethnicity, which may well have encouraged people to respond more on the basis of culture than actual beliefs or religious affiliation.

Ethnicity question before Religion question in 2001 Census

Other surveys tend to give around 30 – 40% non-religious, rising to 60 – 65% for young people. See BHA selection of statistics on religion and belief in the UK.

The BHA also says "Apart from the inaccuracy of the data collected on religious affiliation, there are real, practical problems with the use of such data. The Census data on religion says nothing about the actual religious practice, involvement, belief or belonging of the population. However, both central and local government use such data in resource allocation and for targeting equality initiatives. And the figure stating that 72% of the population are ‘Christian’ has been used in a variety of ways, such as to justify the continuing presence of Bishops in the House of Lords, to justify the state-funding of faith schools (and their expansion), to justify and increase religious broadcasting and to exclude the voices of humanists in Parliament and elsewhere.

The question is not fit for the purposes for which it was included, for the first time, in 2001."

So what does the Religion question really measure? See the BHA Census Campaign.