2021 United Kingdom census

On 21 March 2021, the censuses of England and Wales and of Northern Ireland took place. The census of Scotland is planned to take place in 2022. Censuses have been done in the United Kingdom every 10 years since 1841. They are now run by the Office for National Statistics.
Changes from 2011 census.
The general style of the questionnaire is similar to that of the 2011 census, although there are some new questions for 2021:
Most of it was done online, the first time this has happened.
Amended Legislation.
In Scotland, the Census (Amendment) (Scotland) Act 2019 makes provisions for voluntary questions about transgender status and sexual orientation to be asked. The Census (Return Particulars and Removal of Penalties) Act 2019 makes the same provision for England and Wales. The sexual orientation question will also be asked in Northern Ireland.
On 17 March 2021, the ONS withdrew from the High Court proceedings, conceding that "what is your sex" refers to sex as recognised by the law, and not gender identity.