Inflation revision latest in series of data issues to affect ONS

The revision of April’s headline rate of inflation following the discovery of an error is the latest in a handful of data issues to affect the work of the Office for National Statistics (ONS).

The agency produces a huge number of reports, forecasts and projections every year, ranging from migration and population estimates to the most popular baby names.

But recently the ONS has had to warn its users about the reliability and interpretation of certain data, while also pausing the publication of some figures.

Gender estimates in 2021 census

The ONS said in April 2025 that figures from the 2021 census showing the estimated size of the transgender population in local areas of England and Wales should not be used.

This was because language barriers may have led some respondents to misunderstand the census question: “Is the gender you identify with the same as your sex registered at birth?”

The agency first acknowledged in 2023 that the question may have caused some confusion and the following year it downgraded the gender census data from official statistics to “official statistics in development”.

The 2021 census was the first of its kind to include a voluntary question on gender identity.

In guidance published in April this year, the ONS said the census could still be used to give a “broad indication” of the overall size of the trans population in England and Wales, estimated to be 0.5% of the total population aged 16 and over, or 262,000 people.

But it said the data “should not be used” to estimate local trans populations, adding that some people – “notably those with lower levels of English language proficiency” – may have unintentionally said they had a gender identity different from their sex registered at birth.

The ONS said it was engaging in work across the UK “to build a robust and detailed understanding of user and respondent needs on the topics of sex and gender identity”, with findings to be published later this year.

They said next steps will include decisions about designing “prototype questions to be tested, refined based on feedback and tested again with a range of people”.

Workforce estimates

The ONS has for several years warned against the reliability of its estimates of the UK workforce, including employment and unemployment rates as well as levels of economic inactivity.

This is because of problems with the Labour Force Survey (LFS), which the ONS uses to produce its estimates and which collects information from a sample of households each quarter.

The response rate to the survey dropped sharply during and after the Covid-19 pandemic, falling as low as 17% in 2023, leading to the data losing its status as official statistics.

In February 2025, the then head of the ONS Sir Ian Diamond told a committee of MPs “I lie awake worrying about this”, adding that he was “super hopeful” a revamped version of the survey would be up and running in 2026.

Bank of England boss Andrew Bailey has said the quality of the figures is a “substantial problem”.

Economists at the Resolution Foundation think tank recently suggested the survey may have underestimated growth in employment by 930,000 workers since 2019.

Producer inflation

In March 2025 the ONS announced it was pausing the publication of its producer price inflation data, due to an issue with the way the figures were calculated.

Producer price inflation, often known as “factory gate prices”, reflects the changes in the price for goods and services bought and sold by manufacturers and the service sector.

The problem was found to affect the period from December 2008, with the main impact on producer price inflation rates in 2022 and 2023.

Because this data is used by the ONS to help it estimate economic growth (GDP), the agency said that correcting the figures “may lead to impacts on the level of estimated output in some industries, with revisions to estimates for services, production and construction particularly likely in 2022 and 2023.”

Estimates of consumer price inflation were not affected by this issue.

The ONS said it hoped to restart publication of monthly producer price inflation in summer 2025.

Consumer inflation

The most recent issue identified by the ONS is to do with its estimates of consumer prices inflation (CPI).

An error was identified in the Vehicle Excise Duty (VED) data provided to the ONS by the Department for Transport, which is used to calculate CPI.

The incorrect data overstated the number of vehicles subject to VED rates applicable in the first year of registration.

This in turn led to an overstating of the headline CPI rate for April 2025, which was initially estimated to be 3.5% but has now been revised down to 3.4%.

The ONS said it would be using the correctly weighted data from May 2025’s figures onwards, meaning no further statistics would be affected.