the liberal democrats will vow to protect the entire education budget in the next parliament ` from cradle to college ' .
unlike tory and labour plans , spending would rise per pupil or with an extra 460,000 schoolchildren expected in the next five years .
but mr clegg will say this is a deal-breaker in any future coalition talks after may 7 , in order to win over ` centre-ground ' conservative voters worried about funding cuts for schools .