Two in five of sixth form colleges could close under Tory cuts worth at least £1.6bn, Labour has warned.
The government has launched area reviews into post-16 educational institutions, which Labour says "makes clear their intention to close down some colleges". New analysis from the House of Commons Library, which was commissioned by Labour to model the effect of a 25% cut on college budgets, found the four in 10 further education institutions would be under threat.
Labour says college budgets are not protected and might face huge funding cuts in George Osborne's 2015 Spending Review, which is unveiled later this month.
Shadow education secretary Lucy Powell MP said the government is putting post-16 education on a cliff edge.
"It is simply not possible to build a 21st century economy on falling investment in education," she said. "Under the Tories, [post-16 education] faces cuts, putting four in 10 colleges under threat of closure."
Powell continued: "This country’s future success depends upon making sure every young person has the opportunities they need to fulfil their potential. At the moment, the government’s narrow and backward-looking plan for education is simply not up to that task."
Sixth form college leaders previously said they feared for their futures and had been left on "starvation rations".
Almost 40% of sixth form headteachers said it was likely their college will cease to exist in the next five years, with seven in 10 said they cannot provide students with a quality education with the funding assigned to them next year.
James Kewin, deputy chief executive of the Sixth Form Colleges’ Association described the report as "deeply worrying".
"This confirms our fears that some Sixth Form Colleges could be wiped from the educational map after the spending review," he said. "Funding for 16-19 year olds - already significantly lower than for younger students - has been cut three times since 2011 and it seems certain that further reductions will be made next year.
“The evidence is clear – Sixth Form Colleges outperform school and academy sixth forms while educating more disadvantaged students and receiving less funding.
"And yet the government is simultaneously committed to reducing the number of Sixth Form Colleges through the area review process while increasing the number of school and academy sixth forms to meet its manifesto commitments."
Shakira Martin, NUS' vice president for further education, said she was "ashamed" to live in a country where the government shows "such disregard" to learners.
"Cutting money in FE means cutting the future of hundreds of families. It will stop the most marginalised in our communities achieving," Martin said.
"It can’t just be A-Levels or apprenticeships. We don’t want an education system which allows one group of people to sail through an elite system while the rest of us struggle.
"Colleges are lifelines to the communities they serve. Going back into college as an adult saved my life and it saved my family. If I hadn’t been able to return to education as a young mother and get the qualifications I did, I don’t know what would have happened to me."
A Department for Education spokesperson said: "We are determined that post-16 providers have the resources they need to ensure young people in further education can enjoy high quality courses."