We don’t know exactly how many houses we will build.

The residents of East Lindsey must have been in for a shock last year. According to the census update, it was not, as previous numbers suggest, in the mostly rural Lincolnshire district around the seaside resort of Skegness, about 390 houses are built every year; There were 2,330.

Yet from the top of the Odyssey – the local amusement park’s tallest rollercoaster – you’d struggle to see any sign of these new housing developments: no more cranes peppering the horizon or roads clogged with trucks. No boom. In the local population, either. So where are they?

A closer look at the census data reveals one clue: the re-counting added many of the stationary holidaymakers stationed near the North Shore to housing.

It’s not clear if these holidaymakers are due to an increase or an underestimation of previous data, or if there’s some sort of allocation issue, but it points to an inconvenient and often overlooked truth: We don’t really know how many new homes there are. We build in England every year. And the number depends on who you ask.

For a government with a clear housebuilding target – 1.5 million new homes by 2029 – this is a problem. And it represents another area to add to immigration and employment where the quality of official statistics is very poor.

If you go to the Office for National Statistics website and download the house building data for England, politicians, journalists and even housing academics will be using data that is not fit for purpose. Although the primary source – the Ministry of Housing, Communities and Local Government – will fail you if you click on the wrong link – the most commonly used house building data for this country actually shows new building completions. And in great measure.

ONS data is largely based on Building Control figures, a market historically dominated by the National House Building Council (NHBC) – an organization set up in the 1930s to insure new homes due to concerns about poor construction quality. However, over the past two decades, NHBC’s market share has been declining – from 85 percent to about 60 percent. Although Building Control data has improved slightly since 2017, there is a significant underestimation, with no reliance on NHBC data.

There are more robust new homes published as part of the Government’s Additional Housing (NAD) reports. This allows us to understand both the balance and the number position in the building control data. For example, it shows there were around 158,000 completions across England in the 2023-24 financial year, while the more accurate NAD completions figure is 199,000 – a 25 per cent difference, or 40,000, almost a washout.

The minimum number is greatest in areas with many home builders. While the long-term trend has been the increasing dominance of large, listed homebuilders, the market has become more diversified over the past decade. In many places, there has been increased activity in everything from small house builders and housing associations, to build-to-rent investors and luxury developers – at least until interest rates start to rise. And it seems they are looking elsewhere for their construction warranty.

This means that the building control information for London is very wrong. For 2023-4, NHBC data shows there were around 16,000 new build completions, while NAD figures show more than 28,000 – the more comprehensive Greater London Authority data says there were around 32,000 builds. So building control information seems to be missing from around half of the London house building market!

Building control data is still very useful in markets where the traditional volume of home builders still dominates – for example, suburban construction on the outskirts of the city. Although, in places such as Milton Keynes, where there has traditionally been a good relationship between building control and NAD data, there are signs of failure in recent years as rent-to-own developers and others move in.

It’s not just England struggling to count how many homes it’s building: Ireland has previously overestimated housing supply because it relies on electricity connections to count new properties. Repurposed ranches, homes, and vacant homes contributed to this. High housing supply figures. When the method was revised in 2018, it reduced the number to about 58 percent.

Measuring how many houses we are building is not only important for the sake of government. Housing targets (They are actually based on net additions, a measure that includes changes in usage and changes). Understanding who is building new homes and where is important to ensure policies are fit for purpose – and not just about hitting targets.

It can also affect your own investments. A growing number of UK pension funds are investing in residential property, particularly through the build-to-rent market. A lack of accurate public information about who is building what and where will prevent their investment from performing as expected. Meanwhile, other firms, including one major, listed housebuilder, still refer to building control data in London to highlight the capital’s vast housing supply. The volume of supply relative to targets is still high but not as large as you regularly suggest.

And while the NAD data is a clear improvement over the BC numbers, even that isn’t perfect. It is published only annually and with a delay of eight months. According to London’s GLA data, the lack of historical revisions before 2019-20 means the data probably underestimates completions as some take longer to register. We also don’t know exactly how far back the undercount goes. The late Dr. Alan Holmans, an expert in housing statistics, expressed doubt that housing completions in the 1990s—perhaps even earlier—were fully recorded.

To deal with missing completions, NAD data is updated every 10 years when the latest census is released. However, we don’t know whether the missing homes are newly built or from another source, and we don’t know what type of property they are or who built them – so the collapse in East Lindsey, where the number of homes has increased, will account for a third of the national adjustment of 5,890 homes a year between the 2011 and 2021 census. It holds.

If nothing else, it shows that if the Government really want to hit their house building targets this Parliament, maybe they should focus on building for holidaymakers who don’t move outside of Skegness.

Neal Hudson is a housing market analyst and founder of BuiltPlace, a consulting firm.