UK car tax error overstated inflation by 10 basis points, ONS says

The UK's Office for National Statistics (ONS) announced that an error in government-provided car tax data led to an overstatement of the consumer price inflation rate by 0.1 percentage points for the year to April; the retail price index and CPIH were also overstated by 10 basis points. While the ONS will not amend the statistics, it is reviewing data quality assurance processes, adding to existing scrutiny of the agency's data reliability amid an ongoing government investigation into official economic data effectiveness.

Analysis

The UK's Office for National Statistics (ONS) has disclosed an error in car tax data that resulted in a 0.1 percentage point overstatement of the Consumer Price Inflation (CPI) rate for the year to April, meaning the actual rate was 3.4% rather than the initially reported 3.5%. Similarly, the Retail Price Index (RPI), critical for index-linked gilt payments, and the CPIH measure including owner occupiers' housing costs, were both overstated by 10 basis points. The ONS has stated these historical statistics will not be amended, though corrective measures will ensure accurately weighted data from May figures onwards. This incident exacerbates existing concerns regarding the reliability of ONS data, particularly following criticisms of its labour market figures and amidst an ongoing government investigation into the effectiveness of official economic data publication. The ONS's commitment to reviewing its quality assurance processes for external data is noted, but the repeated data issues raise questions about the integrity of key economic indicators used for policy-making and investment decisions.

Key Decisions for Investors

• Investors should factor in a heightened degree of uncertainty when relying on UK official economic statistics, particularly inflation data, given this error compounds existing credibility concerns surrounding the ONS.
• While the 0.1 percentage point revision to April's CPI is marginal, those with exposure to RPI-linked instruments should note the 10 basis point overstatement for April will not be officially corrected in past figures, though future RPI calculations from May will use the accurate data, warranting close monitoring of upcoming releases.
• Consider the potential for increased volatility or mispricing in markets sensitive to UK inflation data until the ONS demonstrates consistent improvements in its data quality assurance and the government's investigation yields tangible reforms.