Much of Britain on Sunday conducts a once-in-a-decade census, for the first time completed primarily online and which will ask about gender identity to help develop policy, services and "further equality."
The census will be held in England, Wales and Northern Ireland to gather detailed information on the country's population, their characteristics, education, religion, ethnicity, working life and health.
It was postponed in Scotland until next year due to the pandemic, so UK-wide results will be collated later.
The census - the 22nd in British history and last conducted in 2011 - is carried out to help inform decision-makers in national and local government, community groups, charities and businesses.
The compulsory survey is the most important single source of information about the size and characteristics of the country's population.
Traditionally conducted on the doorstep by an army of questioners, this year it will be completed primarily online, in a change spurred by the coronavirus crisis.
Around 90 percent of households have been sent a code to login with online, while some paper copies are also available for those who need them.
People refusing to complete the survey face a fine.
The census has previously asked people for their sex, among other things.
However, respondents aged over 16 can also now provide a voluntary response to an additional question about whether "the gender you identify with (is) the same as your sex registered at birth".
(Source: AFP)