Census 2021 letters begin to land in England, Wales and Northern Ireland – here's what you need to know

The census is a survey that happens every 10 years and gives the Office for National Statistics (ONS) a picture of life in England and Wales. In Northern Ireland, Census Day is also Sunday 21 March but this isn't run by the ONS – instead it's the Northern Ireland Statistics and Research Agency (NISRA). Here's what you need to know: 

• You can complete the census online or by post. Your invitation letter will include a unique access code for your household to complete the census online, or you can ask for a paper form to be posted. See the Census England and Wales and Census Northern Ireland websites for details on how to request a postal form, including if you've not yet had your invitation letter.  

• You can be fined up to £1,000 if you don't complete the census. It's an offence to supply false information or not to complete the census, and you could be fined up to £1,000. Fines are a last resort though. In England and Wales, four people received the maximum £1,000 fine for non-compliance at the last census in 2011, while a further 270 people were fined an average of £218.

• You can submit answers privately without people in your household seeing. You can apply for an individual access code via the websites listed above – you can choose to receive it by text or post. 

• Most questions are compulsory. The form will indicate which questions you must complete and which are voluntary. In England and Wales, for example, the ONS told us all questions except those on religion, sexual orientation and gender identity are compulsory.

• You technically should complete the form on Sunday 21 March (though most can do it earlier). That's because this is the day being used as a snapshot of life in 2021. If you can't complete the form on the day itself, do so as soon as you can afterwards but fill it in based on your circumstances on 21 March. You can complete forms online until early May. You can technically fill in the form before 21 March if your circumstances won't change, but contact the ONS or the NISRA if you do so and anything subsequently changes before Census Day.

• In Scotland, the next census takes place in 2022. Visit the National Records of Scotland's census website to find out more.