The Liberal Democrats will fight the next general election on a promise to protect education spending from children's earliest years to the time they go to college, Nick Clegg has said.
The Deputy Prime Minister said that extending the existing "ring fence" on schools spending to cover the whole of the education budget from the ages of two to 19 would cost an additional £10 billion a year, rising annually with inflation.
"Liberal Democrats will protect the full education budget, from the cradle to the college," Mr Clegg told a Westminster news conference.
"Money invested in our children is the best investment of all because education can really transform lives. We believe education should be properly funded because education is the very core of a liberal society."
Mr Clegg would not be drawn on whether it would be a "die-in-the-ditch" commitment for the Lib Dems in any future coalition talks.
He said the party would spell out how it would be funded closer to the time of the general election next May.
"My challenge to Labour and the Conservatives is if you are not going to do this, what are you going to cut? Are you going to cut money to colleges? Are you going to cut apprentices? Are you going to cut help for toddlers?" he said.
"I think it would be unimaginable for us as a country, having made these steps, to reverse them."
Mr Clegg has promised a regular "drumbeat" of policy announcements over the summer as his shattered party tries to rebuild support following its hammering in last month's European and English local council elections.