Plans for the first ever "primarily online" census have been unveiled by the Government.

Ministers announced that the next survey of households in England and Wales is due to take place on March 21 2021, subject to parliamentary approval.

In what is billed as a "digital-first" census, up to three quarters of respondents are expected to complete the questionnaire on the internet.

A white paper published by the Cabinet Office on Friday also confirmed previously reported proposals to include new questions on sexual orientation and gender identity.

Sir David Norgrove, chairman of the UK Statistics Authority, said: "The census is the foundation for national and local policy, for planning and for targeting resources.

"The information gathered on the population, people's characteristics, education, working life and health, enables public services and businesses to properly serve our communities.

"The political context has changed substantially since the last census in 2011, including through the decision for the UK to withdraw from the European Union, and this has strengthened the need for a deeper understanding of the communities we live in and how they are changing."

First taken in 1801, the census collects information about the population every 10 years.

Chloe Smith, minister for the constitution, said that in 2021 it will be, for the first time, a "primarily online census".

Provision will be made for those unable to fill in the census online, she added.

The white paper said: "Based on previous and international census experience of online collection, and predictions of the digital take-up of services, ONS (Office for National Statistics) is planning that around 75% of all household responses will be online.

"However, the actual take-up of this channel is uncertain and the capacity planning for the response system will allow for flexibility."

In advance of every census, consideration is given to new questions which could be added to provide information which is not available from elsewhere.

Following consultation, statisticians have proposed that there will be a new voluntary question on sexual orientation for those aged 16 and over.

The ONS said testing has shown that it would be acceptable to include the question and that it will "deliver good-quality data with minimal effect on overall response and respondent burden".

In addition to the usual question on being male or female, there will also be a voluntary question on gender identity for people aged 16 and over.

The 2021 census will, for the first time, collect information on past service in the UK armed forces.

"The new topics will all help government bodies by meeting the need for better quality information for monitoring equality impacts on communities," the white paper said.

Consideration was given to adding questions on volunteering and income, but the ONS is not recommending these for inclusion.

A census rehearsal is planned for October next year.

National Statistician John Pullinger said: "The census is for everyone; it gives us all the opportunity to stand up and be counted in democratic debate and policy decisions."