The Office for National Statistics (ONS) has been coming under pressure for a string of issues with its economic data, which is routinely used by the country's policymakers.
On Friday, it admitted to a mistake over how it adjusts its retail sales data to align precisely with calendar months, such as to account for Easter which occurs on a different date each year.
An annual review found that figures had not been adjusted correctly, the ONS said.
ONS director general of economic statistics James Benford explained that it had resulted in previous figures "overstating the monthly volatility in retail sales" in the first half of 2025.
This included correcting June's retail sales volumes to a 0.3% increase, down from a previous 0.9% increase.
May's sales drop was revised to a 1% decline from the previous 2.8%.
Revisions to April's data resulted in retail sales volumes swinging to a 0.4% decline, having previously been recorded as a 1.7% jump.
On the other hand, March's retail sales were revised up to a 1.2% increase, from a previous 0.2% decline.
Rob Wood, chief UK economist for Pantheon Macroeconomics, said that "major revisions" mean retail sales figures were lower over the first half of 2025.
He said: "Official retail sales volumes growth now averages 0.2% month to month in the first half of 2025, compared to 0.3% previously.
"Weaker sales growth on average this year points to consumers reluctant to spend, which could challenge the growth outlook."
He said there were signs that households have "rebuilt their rainy day savings and are cutting back on the amount of money they squirrel away each month, which should help support spending" going forward.
The ONS's Mr Benford said: "I apologise for the delay to this release and for the errors in how we have been seasonally adjusting these data.
"Our economic statistics and surveys improvement plans will put more resources into improving the quality of our statistics and provide a basis for open reporting to users about the nature and timing of further improvements."
The error is the latest in a line of setbacks for the statistics body.
It has been particularly under fire for issues related to its labour market data, with recent criticism from Bank of England and Treasury officials.
Late last year, the organisation said it might not be able to replace its current labour force survey with a more accurate version until 2027.
There have also been delays and major adjustments to the ONS's trade data and producer price figures this year.
In June, a review led by Sir Robert Devereux found there were "deep-seated" issues with the statistics body and called for a major overhaul.
Darren Tierney was appointed permanent secretary of the ONS last month to lead the body as it undergoes reforms to its culture and management, and works to improve the accuracy of key statistics.