Image caption Jules White has co-ordinated a campaign over school funding that now reaches millions

Head teachers are usually known for getting people to stay in line, but Jules White has become a relentless rebel over school funding.

The Horsham head teacher has co-ordinated a letter warning of school cash shortages, which will reach 2.5 million homes on Thursday.

This direct line to parents' kitchen tables has put MPs under pressure.

And Mr White, along with 4,000 other heads sending the letter, won't stop until they get £1bn extra funding.

The head teacher of Tanbridge House School, in West Sussex, has formed a formidable lobbying operation over what he says is an unresolved crisis in school funding in England.

"It causes enormous anxiety and stress, trying to see how your school can run to the standards everyone expects," says Mr White.

"The system is under massive duress."

He distils this into two basic issues: "Not enough money, not enough teachers."

Enough extra?

Heads in local authorities from Cornwall to Norfolk have been protesting and contacting parents - pushing school funding up the list of issues facing MPs on the doorstep during the general election.

Image copyright Getty Images Image caption Schools have been promised more money, but heads say it is not enough to make a difference

The government responded after the election by finding £1.3bn within the Department for Education's budget to be put into front-line spending on schools.

Schools funding has been protected in real terms for the next two years, alongside a new funding formula for sharing out the money.

But Mr White and his fellow head teachers remain unimpressed and have written to parents to say: "This is not enough to make a real difference."

"We were going bankrupt," says Mr White. "Now we're out of the financial gutter. We may be able to survive better."

The heads' campaign says that another £1bn over two years is needed for schools to have sustainable budgets.

"The only way you can make it work is to put back the money that has been taken out."

State school funding £42.4bn What the Government is setting aside for schools in 2018-19 £1.3bn more than was already promised for the two years to 2020 9,000+ state schools had budget deficits in 2015-16, according to government figures

4,000 of those schools have been in deficit for two years.

88% of schools will have lost funding in real terms between 2015-20, according to a coalition of teachers' unions Getty

There remain big regional differences in schools facing similar levels of deprivation.

Mr White says his own school budget is £6.7m per year, but an equivalent school in inner London could receive £9.6m.

The consequence is bigger class sizes, staff cuts and fewer support services.

'Relentlessly reasonable'

The letter to parents highlights the difference in funding levels - with a secondary school in Hackney in east London getting £4.4m more than one in York.

It says a primary school in Greenwich in London receives almost £500,000 more per year than one in West Sussex.

Image copyright PA Image caption Parents were protesting over school funding before the election

Mr White says he is a reluctant campaigner.

"I genuinely don't want to do this." But he says he has been driven by the "injustice" of the financial problems facing schools.

"We have been relentlessly reasonable.

"This is not some group of political wackos expecting everything to be lined with gold."

So the heads have begun their campaign again - telling parents to make their voices heard with MPs.

All of this is leading towards the Autumn Budget in November and big decisions for the chancellor.

But the Department for Education says that significant steps have already been taken to resolving funding inequalities.

The National Funding Formula "has been widely welcomed and will put an end to the historic disparities in the system", said a Department for Education spokesman.

"As the independent Institute for Fiscal Studies has confirmed, overall schools funding is being protected at a national level in real terms per pupil over the next two years.

"Our formula will provide significant gains for under-funded schools of up to 3% per pupil in 2018-19 and a further 3% in 2019-20."