The startling claim was made during a phone-in on James O'Brien's LBC show earlier this week.
In the call with O'Brien, who grew up in Kidderminster, headteacher Sean Maher explained the situation at his school.
He started off with saying that the current circumstances were the bleakest he's faced in 10 years as a headteacher, during which he's also dealt with austerity and Covid, and that the frustration for many was that this was not down to financial mismanagement.
"I left for my summer holidays this year with a balanced budget and fully staffed school, I came back to looking at an in-year £250,000 deficit because of unfunded pay rises passed on by the government, because of increased energy costs," he explained.
Mr Maher is headteacher of a south-west London secondary school of 1,100 pupils, and warned that schools like his can't make those savings without "drastic decisions". He said at his school they'd have to use every penny they've saved or hoping to use on construction projects to get the school through the current academic year.
"But for next year the only way I can find an extra £300,000, which is the ball-park figure of what we think we will need to save without some government intervention, is by reducing staffing," he said.
"And if I'm reducing staffing I'm either going to have to increase class sizes or I'm going to have to cut the curriculum offered."
Mr Maher said there's never been a time when the need for at-risk subjects such as art, drama, music and sport has been so obvious.
"Coming out of Covid, how can we not invest in our young people now? That is the frustration," he added.
Mr Maher said teachers and support staff deserved more pay but there needed to be government investment, and that budgets are planned year-to-year before the end of the summer term.
"If extra costs are passed on after that there's no extra money sloshing around that we can suddenly just dip into and say 'I'll put another £250,000 in my salaries budget', it just can't be done," he said.
When asked about energy, the headteacher said his school is facing massively increased costs and although there is help, he doesn't know how much or for how long.
He continued: "At the moment we haven't got the heating on in school and I've told the caretaker not to turn it on until we've got some better answers on that.
"And the other thing is increased food costs. We're desperately trying to hold our food prices down because what we don't want to do is to pass on any extra costs if we can avoid it to our families because they are struggling enough already."
He then added: "But it comes to something when you feel like the government is working against you giving the best education to young people."
The comment left O'Brien stunned, with Mr Maher reaffirming that he is "battling" the government, saying he'd do anything for the school and his pupils but there was "a limit".
After the call Mr Maher tweeted: "I don't really want to have to fight this fight, I have other things that need my attention, but our young people are worth more."
His call gained plenty of support, with people describing his words as "heartbreaking" and "powerful".