Image caption Head teachers from the Worth Less? campaign brought their message to Downing St

Head teachers representing more than 5,000 schools across England are supporting a protest letter to the chancellor over "inadequate" funding.

The letter, being delivered to Downing Street, warns of schools increasingly having to make "desperate requests to parents for 'voluntary' donations".

Heads are calling for an extra £1.7bn per year for schools.

The government has already moved £1.3bn of education funding directly into school budgets.

The protest, ahead of next week's Budget, has been organised by regional groups of head teachers representing schools with 3.5 million pupils in 30 local authorities from Cornwall to Cumbria.

It follows a letter warning about funding cuts, sent to the parents of more than 2.5 million pupils in September.

This is the biggest collective protest so far from the school funding campaigners, who have been warning of an overall lack of investment and a failure to resolve differences in levels of per pupil spending.

Funding differences

"It is extraordinary that some English secondary schools will receive 60% less funding than others of the same size," says the letter to Chancellor Philip Hammond.

"The impact on class sizes, curriculum offer and staffing is obvious," the heads write. "A school receiving over £4m more than another could, for example, afford 133 more teachers."

Image caption West Sussex head Jules White co-ordinated a funding warning sent to 2.5 million families

The government has recognised the regional anomalies in funding and published a new national funding formula.

But the heads argue that changes in how funding is allocated will depend on there being enough overall money in the system.

Despite the promise to move £1.3bn from the Department for Education's budget directly into school spending, the heads say they will still have faced a real-terms cut of £1.7bn between 2015 and 2020.

Without this £1.7bn being restored, heads are warning the chancellor:

they will not be able to afford to recruit teachers

class sizes will rise

subjects will have to be withdrawn

sixth forms could close

special needs pupils will not get the support they need

Labour's shadow education secretary Angela Rayner said the government "needs to start listening to head teachers and concerned parents".

"Despite Tory spin, the new funding formula does nothing to reverse the cuts to budgets and every penny they have found just comes from cutting other education provision - it isn't fair, and it isn't funded."

But school standards minister, Nick Gibb, said the £1.3bn being put into school budgets "will put an end to historic disparities in the system".

"There are no cuts in funding - every school will see an increase in funding through the formula from 2018, with secondary schools set to receive at least £4,800 per pupil by 2019-20.

"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."