Jules White has never joined a political party. Nor has the West Sussex headteacher ever taken part in a sit-in, or any sort of industrial action.

As a student at the University of Essex, a well-known radicalist hotbed, he spurned activism in favour of “playing football, playing cricket, and going out”.

And until he launched the national school funding campaign WorthLess?, he had never so much as attended a protest.

Now White regularly rallies thousands of other heads across 40 local authorities and can, in the ping of an email, reach 6 million families, via a national network of WorthLess? members. The campaign can justifiably take some of the credit for pushing the government into a decision, announced after last year’s general election, to boost school budgets by more than £1 billion.

But speaking out has brought some unwelcome attention; White says he has been subject to “intimidating” messages and behaviour from officials and senior politicians.

So why did a self-professed “regular bloke” leading a successful secondary school - the “outstanding”-rated Tanbridge House, in Horsham - take it upon himself to become one of the most prolific campaigners in a such an acrimonious battle?

West Sussex is one of the lowest-funded local educational authorities in the country but, on the surface, White’s school doesn’t appear to be crying out for money. In between lessons, pupils - only 11 per cent of whom have been eligible for free school meals over the past six years - walk purposefully across a leafy courtyard set in the middle of airy buildings that benefited from a £5.75 million expansion a couple of years ago.

But appearances can be deceptive.

“I was driving home on a Friday at 7pm, listening to local radio,” says White, who had arrived at work that day at 6.45am, as usual.

“I was thinking, ‘I’ve got a hell of a lot going for me in this school. It’s about as good as it gets in state education - but we’re clinging on. I can’t get maths and English teachers, my class sizes are rising, I’ve got absolutely no money, I’ve not got enough TAs to cover kids with statements. We’re cut to the bone.’”

Cuts to local authority budgets have left safeguarding gaps, he says, meaning that he and his senior leadership team frequently have to deal with crises out-of-hours, with no support from other professionals.

“And there was some fella from the DfE chatting on the radio and he started spouting on, [saying] that there’s never been more money spent in education, and there are more teachers than ever,” says White.

It was a turning point for White, who doesn’t shy away from a bit of blue language, and he found himself “effing and blinding” at the radio. He emailed a local news presenter and offered to do a live interview to counter the “clueless” DfE official’s claims.

Things soon snowballed. White spoke to his local headteachers, urging them to speak out collectively about the situations facing their schools: one of them took on Piers Morgan on morning TV - resulting in the bullish presenter uncharacteristically backing down and agreeing that there was a problem.

Headteachers in Essex contacted White to ask if they could get involved, and this rippled out to dozens of other local authorities.

For someone with no previous experience of campaigning, White seems unusually skilled at marshalling thousands of geographically dispersed individuals, and coming up with eye-catching ideas.

One of these involved the Treasury being “invoiced” for £3.5 billion - the amount campaigners say they would receive under a fairer funding system. Headteachers and - importantly - pupils have also lobbied Downing Street, and White has publicly blasted the DfE’s “insulting” advice on balancing budgets (see bit.ly/InsultDfE).

A campaigning one-man band

Perhaps the most powerful tactic has been the coordinated letters to parents, warning that cash shortages are putting their children’s education at risk.

In a politically febrile environment, this has all helped to make school funding a toxic issue for many MPs.

But, despite the support of more than 6,000 headteachers, WorthLess? remains, essentially, a “one-man band”, says White, who squeezes the campaign into his schedule by getting up at 5am on weekends.

Daring to speak out against the political masters of the day is a professionally risky move for any head, and White’s campaign has not made him universally popular.

He says: “I know that senior people in the DfE are, of course, aware of WorthLess? and me. It has been intimidating at times, and you do receive some very robust emails. Partly from the DfE, perhaps from MPs - and you know you’ve hacked some people off … and they make it quite clear in meetings.”

A head who publicly denigrates the state of their school finances may also fail to endear themselves to local parents, he acknowledges. “I spent 18 months on the telly saying, ‘My class sizes are going up. It’s all pretty difficult. I’ve got one art teacher for 1,500 kids.’ It’s not the ideal marketing strategy.”

White admits that a headteacher in a more vulnerable position may not have felt able to take a stand. He is well-established in the local community, having led Tanbridge House for 10 years, taking it from a “classic coasting school” which struggled to attract pupils and which, he says, had a reputation for terrible behaviour, to an over-subscribed one with a top Ofsted rating and an above-average Progress 8 score.

For two years, he focused relentlessly on punctuality, uniform and teachers being prepared for lessons. Even today, when a pupil dawdles momentarily on the way to class, he’s met with a sharp rebuke from White.

His unapologetic fixation on what he calls “basic standards” stems from his own experience as a pupil at a secondary modern in Salisbury.

“Looking back, my school was bloomin’ tough - there were some bloody tough kids there,” he says. “There were some proper old scraps and fights.”

Being sporty, and playing for the football team, helped him to stay on the right side of the bullies. But his own schooling has clearly shaped his approach as a head.

“There was some bloody bad behaviour, and sometimes not the greatest teaching. Those sort of things stick with you,” he says.

White’s focus on getting the basics right means that he has no time for what he sees as “extraneous stuff” that diverts money away from frontline budgets - like the £75 million Teaching and Leadership Innovation Fund - and “an obsession with structures”.

He says: “When we first got our ‘outstanding’ badge, I had someone from the DfE - she rang me up once every two weeks - saying, ‘Jules, would you like to become an academy?’ I’m not interested.

“Why spend another £50,000 on legal fees turning my school into an academy, when my school is regarded as ‘outstanding’ anyway? There’s money in the DfE - they don’t have to spend it on those things.”

White clearly has strong personal opinions on a range of education issues, and one of his achievements has been to keep them separate from his politically neutral funding campaign. In this interview, he generally keeps his tone light, but there is a simmering anger behind many of his words.

‘Of course, they don’t believe in it’

One of his particular bugbears is how schools minister Nick Gibb and education secretary Damian Hinds refuse to admit in public that schools are short of money.

“Obviously we’re pragmatic, they’re not going to go out to the public and say, ‘Everything’s in crisis,’” he says.

“They have to articulate stuff in a sensible and reasonable way. But the disaffection they’ve caused, and the complete lack of trust, in saying, ‘More money than ever before is going into schools, the NFF [National Funding Formula] is giving everyone a rise in real terms.’ It’s at best disingenuous; at worst, deliberately misleading … I can’t stand bullshit.

“Of course, they don’t believe in it. They absolutely know there are schools on the breadline.”

The partly funded 2018-19 pay award for teachers, of up to 3.5 per cent, will force heads to “raid already devastated budgets”, while the DfE will “slash” school support to cover the remaining costs, he fears. The campaign is now at a “pivotal point”, says White.

The overall public spending envelope for the period beyond 2020 will be set out in the Autumn Budget, before the DfE’s share is revealed next year.

A priority for WorthLess? between now and then is to secure an injection of cash into budgets for pupils with special educational needs and disabilities (SEND), including those with “high needs”. In September, 1,000 headteachers are set to gather at Parliament Square to press for this, as well as for a fully funded pay deal for teachers (bit.ly/HeadsRally).

White takes particular pride in the way that his campaign has helped leaders to talk openly about a single, but very pressing, issue affecting nearly every state school in the country. “If WorthLess? has done anything, we’ve given headteachers the confidence to speak out,” he says. “I think that’s the single biggest thing we’ve done.”