The Equalities and Human Rights Commission (EHRC) will ask MPs this week to include a question in the 2011 census on sexual orientation.

The government has previously ruled out asking people to state whether they are straight, gay or bisexual, saying it would be too controversial but the EHRC maintains it is necessary when there are already questions about race and religion.

The Office for National Statistics also believes the question is unnecessary and in 2006, cited concerns about “privacy, acceptability, accuracy [and] conceptual definitions”.

It also argued that people did not want to reveal their sexual orientation in the census and could be put off due to family pressures and embarrassment.

Other critics have said the question, which would ask whether people see themselves as heterosexual, gay, lesbian or bisexual, is overly intrusive and highly personal. It would be optional, rather than compulsory.

Ann Widdecombe, Tory MP for Maidstone and the Weald, told the Times: “It is people’s own business. It is not anyone else’s business and I don’t see why anyone should be asked to declare it.”

However, the EHRC believes the question is vital to ensure that equality legislation is working. According to a paper published by the body, the lack of a question on sexual orientation is “an indication of invisibility” and “a major obstacle to measuring progress on tackling discrimination”.

Every household is legally required to fill out a census form once every ten years and householders face a fine of up to £1,000 for refusing to answer questions.

The 2011 census will ask for the first time whether respondents are in a civil partnership.