Some of Norfolk's cash-strapped high schools could be forced to share subjects, cut staff and lease out empty classrooms to survive a predicted plunge in pupil numbers, the EDP can reveal.

They may also have to compete more fiercely with their neighbours for students as they seek to avoid a damaging downturn.

Smaller schools in rural areas are set to be particularly vulnerable to the predicted 9pc drop in pupil numbers at secondary level in the next five years.

If the Department for Education (DfE) has got its sums right, Norfolk's secondary school pupil numbers will fall from this year's 50,740 to 46,529 by 2015/16.

Primary school pupil numbers in Norfolk, which have been falling in recent years, are set to go in the other direction – up from 56,739 now to 58,377 in 2014/15.

But that will not filter through to secondary schools until the second half of the decade, leaving headteachers, already facing the reality of reduced future funding, to tackle another issue.

Peter Whear, headteacher of Old Buckenham High, said: 'Changing demographics bring about additional financial uncertainty for headteachers at a time of massive cuts in public spending and culture-changing proposals in the recent white paper.

'The problem is particularly acute in rural areas and I am greatly concerned that some headteachers will simply not be able to balance the books.'

Pupil numbers equate to hard cash for schools, with each child worth at least �3,200.

And, despite a government pledge to increase the schools budget by a real terms 0.1pc per year, Mr Whear said it was 'more than offset by a national rise in pupil numbers'.

He added: 'Schools face a serious cut in funding.'

While a number of other areas are set to see a fall in pupils, most will increase, and few are as extreme as the secondary figures for Norfolk.

In Cambridgeshire, numbers are set to remain steady, while in Suffolk, numbers will rise for a few years before falling back from 2014.

Tim Newton, senior development officer at Norfolk County Council for school organisation, said school population went 'in waves'.

He said that when pupil numbers dropped, schools had to 'look at their staffing', and added: 'There are partnership approaches which need to continue. Schools may need to explore partnerships with each other.'