Rishi Sunak has been challenged over his claims to have reduced public debt by the chief of the UK’s statistics watchdog.

The Prime Minister said that “debt is falling” in a social media video and that “we have indeed reduced debt” at Prime Minister’s Questions last month.

But the chairman of the UK Statistics Authority (UKSA) Sir Robert Chote suggested Mr Sunak’s claims were misleading.

In a letter to Liberal Democrat Treasury spokesperson Sarah Olney, he said the average person “would likely have assumed that he was claiming that debt was already falling or that the Government’s policy decisions had lowered it at the fiscal events – 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 said Downing Street told the UKSA Mr Sunak’s claims referred to forecasts by the Office for Budget Responsibility (OBR) that the underlying measure of net debt would be falling as a proportion of GDP in the final year of its five-year forecast, meaning 2028-29 at the time of the November autumn statement.

This was primarily due to happen because of changes to the OBR’s underlying economic and fiscal projections, even as Government decisions on tax and spending pushed debt higher in cash terms.

But, Sir Robert noted, this is not how the “average person in the street” would interpret the Prime Minister’s statements.

“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,” he wrote.

The Office for Statistics Regulation, the UKSA’s regulatory arm, “will work with the Prime Minister’s office to ensure further statements on debt levels adhere to our guidance on intelligent transparency,” Sir Robert said.

Ministers should “ask themselves how someone with an interest but little specialist knowledge is likely to interpret a particular claim and to explain themselves clearly if they choose to depart significantly from that in definitional terms,” he wrote.

Reducing debt is one of Mr Sunak’s five pledges, alongside halving inflation, growing the economy, cutting NHS waiting times and stopping small boat crossings.

Ms Olney had written to the UK’s official statistics watchdog to raise her concerns about Mr Sunak’s remarks.

Following Sir Robert’s reply, Ms Olney said: “Rishi Sunak knows he has no good story to tell on the UK economy so he has resorted to making one up. The least this no-growth Prime Minister could do is be honest about it with the British public.

“Instead, he has reached for the Boris Johnson playbook and is undermining trust in politics. This is desperate stuff from a desperate Prime Minister, and it is right that he has been called out on it.

“Rather than using smoke and mirrors to cover up his own failings, Rishi Sunak needs to come forward with a real strategy to rebuild the economy after the Conservative Party crashed it.”