By Ian Dunt

Atheists are set to launch a campaign calling on people who are not religious to explicitly say so during the next census.

Data from the last census is constantly used by journalists and politicians too promote and defend various policies, but secular groups are concerned that many Brits describe themselves as Christian because of their cultural heritage.

"In 2001 people tended to treat the census question on religion as a question about ethnic heritage," said David Voas, professor of population studies at the University of Manchester.

"Their answers were interpreted very differently, though, by churches, journalists and policy-makers. Which box you tick on the census form may seem trivial, but the results do make a difference in public life."

The campaign, which is being run under the banner 'If you're not religious, for God's sake say so!', is kicking off exactly five months ahead of the next census in England and Wales, which takes place on March 27th 2011.

Organisers at the British Humanist Association (BHA) said they had already raised half of their first funding target on the first day of its launch.

"The flawed wording and the positioning of the religion question in the census in the context of ethnicity encourages people to respond as if they have a religion, and especially over-inflates the 'Christian' category," BHA chief executive Andrew Copson said.

"That would be fine if policy-makers accepted that the results from the census are merely an indicator of broad cultural affiliation.

"But what people do not realise is that by ticking the 'Christian' box rather than the 'no religion' box - which would more accurately reflect their identity - they have contributed to data used to justify an increase in the number of faith schools, the public funding of religious groups, keeping bishops in the House of Lords and the continuation of compulsory worship in schools."

The British Social Attitudes Survey, conducted earlier this year, found 59% did not describe themselves as religious when asked how they would describe their level of religiosity.

It suggested that 62% of people in the UK never attend a religious service and only eight per cent attend a weekly church service.