The head of the UK’s official statistics watchdog has challenged Rishi Sunak over his claim to have reduced public debt, saying the prime minister’s definition of this was so specific and limited that it risked being misleading for voters. Sir Robert Chote, the chair of the UK Statistics Authority (UKSA), said Sunak’s claims last month “may have undermined trust in the government’s use of statistics and quantitative analysis in this area”. Writing to Sarah Olney, the Liberal Democrats’ Treasury spokesperson, Chote said the Office for Statistics Regulation, the UKSA’s regulatory arm, would “work with the prime minister’s office to ensure further statements on debt levels adhere to our guidance on intelligent transparency”. Olney raised the issue with Chote’s office after Sunak said “debt is falling” in a No 10 social media video posted on 7 November, the day of the king’s speech, and then said “we have indeed reduced debt” during prime minister’s questions on 22 November, the day of the autumn statement. Downing Street told the UKSA that both claims referenced forecasts by the Office for Budget Responsibility that net debt would be falling as a proportion of GDP during the final year of the five-year forecast, in the context of the autumn statement meaning 2027-28. In both cases this was mainly happening due to changes to the OBR’s fiscal projections, with government decisions on tax and spending actually making debt higher. Chote’s letter noted that while it was fair to use debt as a proportion of GDP rather than absolute numbers, the “average person in the street” would most likely have taken Sunak’s statement to mean that debt was already dropping and that government decisions had helped do this – “neither of which is the case”. “This has clearly been a source of confusion and may have undermined trust in the government’s use of statistics and quantitative analysis in this area,” he wrote. “Members of the public cannot be expected to understand the minutiae of public finance statistics and the precise combination of definitional choices that might need to be made for a particular claim to be true.” Olney said Sunak had “reached for the Boris Johnson playbook and is undermining trust in politics”. She said: “Rishi Sunak knows he has no good story to tell on the UK economy so he has resorted to making one up. This is desperate stuff from a desperate prime minister and it is right that he has been called out on it.” A government source said: “The OBR is crystal clear – thanks to the long-term decisions we have taken, we are on track to get debt falling.”