LONDON, Sept. 28 (Xinhua) -- Around 1,000 head teachers from across England demanded increased funding for schools during a protest outside the prime minister's office on Friday.

School leaders from about 50 different areas of England joined the rally in Parliament Square before converging on Downing Street, where a delegation delivered a letter to Chancellor of the Exchequer Philip Hammond protesting over what they claim are "unsustainable" funding cuts.

Figures showed the number of secondary schools in England running at a loss had nearly trebled in four years. In July, the Institute for Fiscal Studies said total school spending per pupil fell around 8 percent in real terms in England between 2009-2010 and 2017-2018.

The head teachers complaint is that their budgets have been squeezed by unfunded pay rises, national insurance payments, other cost pressures, and rising pupil numbers.

However, the Department for Education insisted that there is more money going into schools than ever before, rising to a record 43.5 billion pounds (56.6 billion U.S. dollars) by 2020, which is 50 percent more in real terms per pupil than in 2000.