The next national census could be the first to ask people about their sexuality and gender identity, it has emerged.

Demographers are conducting research on whether to include questions on the topics in the next survey for England and Wales, which will be carried out in 2021.

The Office for National Statistics published the results of a public consultation for views on the contents of the census. It said there was a clear need for improved information on sexual identity.

It plans to include a question in a large-scale test next year to assess whether it “has an effect on overall response and to assess the quality of responses”.

Under current assumptions, the question to be used in the trial would ask respondents aged 16 or over which of five options best describes how they think of themselves: heterosexual or straight; gay or lesbian; bisexual; other; or prefer not to say.

The ONS said it aimed to assess the “public acceptability” of asking a question on the topic in 2021.

Statisticians cautioned there was potential for “negative equality impacts”. For example, requesting an individual questionnaire or choosing not to answer the question “could lead to other household members making assumptions about a respondent’s sexual identity”.

If the results of the test prove there are “significant negative equality impacts” or that the information is of “insufficient quality to support positive outcomes” then the question would not be included in the next census.

Gender identity will also be examined as a possible topic after concerns were raised that there was a lack of “robust” data on the trans community.

Campaign group Stonewall told the consultation: “Trans people experience high levels of discrimination and prejudice, yet there is a lack of accurate population data for this group.

“This is a real barrier to researchers, policy-makers and those developing and commissioning services for trans people at a local and national level.”

In its response, the Government Equalities Office said: “The absence of basic data on the transgender population results in the invisibility of transgender inequalities and disadvantage for decision makers and funders.”

The ONS concluded there is a “user need” for data on the topic, and work will include reviewing a finding in a 2009 report that household surveys were not an appropriate approach to collecting information about gender identity.

If questions on sexual and gender identity are included it is expected that an amendment to the Census Act 1920 would be required. Another potential new topic under consideration is volunteering.

The census has collected information about the population every 10 years since 1801. Ian Cope, 2021 census director, said: “Given the unique status of the census, it’s not surprising that there is continued user need for existing topics as well as requests for new topics to be included in 2021.

“As data from the census underpins so many important policies and decisions that affect us all, we need to make sure that people find it straightforward and acceptable to complete.

“We will continue to discuss this balance with everyone who will be relying on the trusted data that the 2021 census will provide, and to test different question options.

“We are also looking at existing sources of administrative data that could provide the information needed without having to include questions in the census.”