Seasonal pattern in UK GDP data raises suspicions among economists

British economic growth data released on Thursday ‌showed ​a marked seasonal pattern for the fourth year in a row, adding to economists' concerns about numbers from the Office for National Statistics.

Last year the ONS was criticised for its data quality in official reports, but these looked mostly at labour force figures which suffered from ‌a fall in response rates, rather than gross domestic product. Thursday's official figures showed that economic growth in 2025 was its fastest in the first quarter, second-fastest in the second quarter and third or fourth-fastest in the third and fourth quarters - as it has been each year since 2022.

In the October-to-December period of 2025, quarterly growth was a weak 0.1%, compared with a strong 0.7% in the ‌first quarter. While this pattern would not be unusual as a one-off due to a downturn in a particular year, the repeated pattern has raised concerns among economists that a problem with ‌the ONS' seasonal adjustment of data has developed since the COVID-19 pandemic.

Statistics agencies in almost all countries make seasonal adjustments to smooth out regular variations caused by Christmas shopping, winter demand for heating, summer tourism and other such factors that distort the underlying trend. But some economists say this process appears to have stopped working so well for British data since 2022, making it harder to forecast future trends and sometimes making it look as if the economy was ⁠close to ​recession when it was not.

"It's very clear that, ⁠since the pandemic, the first quarter and second quarter have been much stronger than the third and fourth quarter," Matt Swannell, chief economic adviser at forecasters EY ITEM Club, said. "It gives a distorted pattern of how the UK ⁠economy is performing, so that makes understanding the growth outlook for policymakers more difficult," he said, adding that it also increased uncertainty over when the Bank of England will next cut rates.

IMPACT OF ONE-OFF EVENTS IN QUESTION Asked ​about the pattern, the ONS said it looked into the issue and a report published in September found no problem when looking at a long historic span of data.

"We ⁠didn't find any cause for concern, but continue to keep our methods under close review," an ONS spokesperson said, adding there had been "a number of one-off events in recent years that have led to the first half of the ⁠year ​looking strong, and the second half less so." In the first quarter of last year there was a surge in exports to the U.S. to avoid incoming tariffs, while economists have also said growth in late 2024 and 2025 was held back by uncertainty about tax increases ahead of finance minister Rachel Reeves' annual budgets.

Swannell said he did not think one-off events were enough ⁠to explain the pattern - which is not seen in other major economies - and the seasonal adjustment processes might not be reflecting changed economic behaviour since the pandemic. James Smith, developed markets ⁠economist at Dutch bank ING, said higher inflation since ⁠2022 might be to blame.

"It's very hard to pin down ... but somewhere in there, I think the data is just not being properly adjusted for the fact that price hikes ... have been more heavily weighted towards the first half of the year," he said. Both Smith and ‌Swannell expect that this year, ‌as in previous years, the official measure of growth will bounce back in the first quarter.

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