Blog Post

Census 2021: Will we know the story of London’s population?

There’s been a lot of discussion over the last few months about whether London’s population is falling, by how much, and who is leaving.

Population estimates like this are notoriously tricky to make in the short term, and estimates about the number of people leaving may partly miss the point: population churn is an entirely normal part of life in London, with hundreds of thousands of people moving out every year, either to other parts of the UK or to other countries. The question perhaps is whether the people who have left will be replaced by incomers as we would usually expect, or whether this flow of new Londoners will dry up.

The 2021 Census, held on March 21 and followed up through the spring and summer, should help us to answer these questions. The results will be significant: the government allocates funding to different parts of the UK based on the numbers of people living in them, and the census is a key source for this. The census is significant in other areas of social policy, too. It tells us not just how many people live in an area but what they are like: their age, ethnicity, employment, how many people they live with, whether they have a car, how they heat their homes, and so on. Towards the end of each census decade, researchers and policy makers often start to get a bit anxious about using census data to drive recommendations — in a fast developing city like London, 2011 feels a very long time ago. 

The census gives us our best and most complete picture of the British population, but it is not perfect – because not everyone fills it in, and because some people make mistakes when they do. Estimating who these people are is tricky, but groups which can be particularly difficult to reach include people who don’t speak English very well, people whose living situation is precarious or changing rapidly, people who live in houses of multiple occupation where they don’t know their housemates well, and people who don’t trust the state with their information. These groups are likely to overlap. The census is anonymous for 100 years and not used for law or immigration enforcement but — despite the best efforts of dedicated survey teams — it’s no surprise that some people don’t quite believe this, especially if they have been treated badly by the immigration system or the police in the UK, or if they have fled persecution abroad. 

This year’s census will be very different to 2011’s. Online completion rates are likely to be much higher, and a lot of people will probably fill it out on a smartphone. Because of the pandemic, census staff will knock on people’s doors to remind them to fill the survey in, but they won’t come into their houses to help them — and of course it’s possible that people will be less willing to speak to a stranger on the doorstep than they have been. Government policy has changed too: “hostile environment” immigration policies in the last decade may have eroded people’s trust in the state, making it harder to engage people who weren’t born here. Estimating the effects of these changes is especially difficult for the census as it’s so infrequent and needs to cover the whole population at once: more regular, sample based surveys like Understanding Society have an advantage as they can test out different ways of increasing responses and implement them quickly.  

There’s a risk that, despite the best efforts of the Office for National Statistics in following up with non-responders and using statistical techniques to understand who they might be, London’s specific population make up together with the effects of the pandemic will mean that this year’s census doesn’t tell us the full story about our city’s population. And 2022, when the first results will come out, could be a tricky time for this to happen: it’s likely that the government will be looking to make savings following very high spending during the pandemic, and the current administration are not very friendly towards spending in London. The fight to get funding for the services that Londoners need might be about to get harder.



Claire Harding is Research Director at Centre for London. Read more from her here.