Extra funding will be available to allow at least a quarter of secondary schools in England to extend the school day, chancellor George Osborne will announce in the Budget today.

The government wants more schools to be able to remain open after the traditional “home time bell” at 3.30pm. They will be able to bid for funding to offer five hours or more a week of additional lessons or extracurricular activities including sports and art.

Ministers say the new flexibility will enable many secondaries to tailor the structure and duration of their school day to suit their pupils’ needs.

The money will come from part of an extra £1.5billion of education funding being announced in the budget today. But the package is unlikely to alleviate the concerns of many schools facing a worrying combination of rising costs and pupil numbers, but real terms budget cuts.

Malcolm Trobe, Interim General Secretary of the Association of School and College Leaders, said: “While we welcome any additional funding for schools, the reality is that the Government has already made savings by requiring schools to pay increased employer National Insurance and pension contributions from existing budgets. This is a significant real-terms cut. The ‘additional’ funding is a classic case of the large print giveth while the small print taketh away.

“It is highly divisive that the funding will only be available to 25 per cent of secondary schools as this will potentially disadvantage children at the three quarters of schools which miss out. Many schools already provide after-school activities so we also need to understand how this new provision will be differentiated from the existing provision and what will be expected of schools.”