Cheshire County Council has written to all chairs of governors saying: "There are potential dangers concerning negligence and liability if there is a serious incident and there is no recognised headteacher or deputy present."
It says schools cannot rely, on a long-term basis, on the appointment of a teacher with extra scale points to fulfil the role. Such teachers cannot fall back on provisions within the teachers' pay and conditions document which give deputy heads clearly delegated responsibilities in the absence of heads.
Three years ago the School Teachers' Review Body dropped its requirement on the number of deputies to allow "greater flexibility". But in practice this has led to a reduction in the number of deputies.
Ron Pearson, Cheshire's personnel consultancy manager, said there has been a marked decline in the number of deputy heads, particularly in the secondary sector.
He said: "We believe schools are deciding to operate without a deputy for financial reasons, but it is essential to have a deputy in the event of a legal challenge.'' The letter has been welcomed by the National Association of Headteachers which has been lobbying the review body for a reversal of its decision on deputy head numbers.
Tom Weston, executive member, said: "As well as the legal worries there is also the matter of professional development. The Government has stressed the need for good leadership in school and is devising a qualification. But if we want well-trained, experienced heads then the post of deputy is essential."