Britain’s statistics watchdog has criticised figures published by a union-backed website in its campaign against school budget cuts.

UK Statistics Authority chair Sir David Norgrove said figures on the School Cuts website risk giving a “misleading” picture of the depth and scale of reductions in funding.

In a letter to Conservative MP James Cleverly, he pointed out three main issues with figures listed in the site, which is backed by the major teachers’ unions.  

• The biggest problem, he said, was that the figures mix past and projected budget cuts, potentially leaving out any future increases for individual schools
• Underlying calculations mix numbers on baseline funding and per-pupil funding from 2015-16 with 2017-18 pupil numbers. “This approach,” said Sir David, “creates a worse picture where pupil numbers are increasing for a particular school.”
• The website’s headline figure that 91 per cent of schools face funding cuts covers only England, but the website suggests it also applies to Wales.

“We believe the headline statement that ‘91% of schools face funding cuts’ risks giving a misleading impression of future changes in school budgets,” Sir David said in the letter.

“The method of calculation may also give a misleading impression of the scale of change for some particular schools.”

This is not the first time the UK Statistics Authority has had to wade into the war of words over the state of school funding.

Late last year Sir David wrote to education secretary Damian Hinds raising “serious concerns” about his department’s use of school funding statistics.

In a “blistering” letter of rebuke, he warned Hinds that he had been forced to intercede with his department four times in the past year over their misuse of data.

The School Cuts website is part of a campaign by leading education unions to push for more funding for cash-strapped schools.

The website lists the NEU, NAHT, GMB, Unison, Unite and the Association of School and College Leaders as backers.

The School Cuts coalition said its figures were accurate and said it would soon release new analysis of the latest government data.

“We stand by our figures,” the group said in a statement. “Some of those cuts have already happened, some are yet to come. All of them are damaging to children’s education.”

Mr Cleverly had written to the authority twice to complain about the website’s use of statistics, which he said were “inaccurate”.

Sir David said he had shared the findings with the website’s analysts, but as they are not official statistics they are under no obligation to change them.