England's biggest education authority has warned it may no longer be possible to have a head for each of its 473 primary schools because recruitment is becoming so difficult.
The news from Kent came as the leader of the largest heads' union criticised other teacher unions for not mentioning the shortage of heads in evidence to the profession's pay review group The number of acting headships in Kent has grown from 23 in September 2003 to nearly 50 last month as the rate of retirement increases and schools find recruiting replacements even harder.
The county council is now considering federating schools to cope with the problem.
A letter from Carol Parsons, Kent's assistant education director, asked primary heads to consider providing short-term leadership in other schools.
"Possibly a time will come in the future when it will no longer be possible to field individual headteachers for all 473 schools," she writes. The letter reveals that Kent already considers amalgamations whenever the headship of a separate infant or junior school becomes vacant.
David Hart, general secretary of the National Association of Head Teachers, said the Rewards and Incentives Group (RIG), comprising representatives from government, employers and four teacher unions, was open to serious criticism for not addressing the problem in joint evidence on pay to the School Teachers' Review Body.
"They made it look as if teacher recruitment is buoyant, but they have not mentioned the recruitment position for the leadership group at all," he said.
This week the Secondary Heads Association submitted supplementary evidence arguing that recruitment of school leaders remained difficult, their responsibilities were increasing and they should receive a higher increase than classroom teachers.
Mr Hart, whose association pulled out of RIG in March, claimed the partner unions had made a tactical error and diluted the case for higher pay for teachers by not making these points.
But John Dunford, general secretary of the SHA, said: "What is important is that we bring this issue to the attention of the STRB and we are quite happy to do that as an individual association." The RIG evidence formed the basis of the Government's case for an annual 2 per cent pay increase, based on the predicted inflation level, for the vast majority of teachers from September 2006 to August 2008.
Overall, the percentage of vacant teaching posts halved between 2001 and 2005 and pay was "no longer the key priority" in seeking to improve recruitment and retention, it said.
And, according to an international report this week, teachers in the UK are among the best paid in the world. An analysis of the teaching workforce in 25 countries shows that only five - Switzerland, Korea, Germany, Japan and the United States - pay more than UK schools.
The Association of Teachers and Lecturers' supplementary submission says it supports the joint evidence, yet is extremely concerned that it may lead to "an unjustifiably optimistic view of the future". It argues for a pay rise significantly above inflation, warning that anything less could see more experienced teachers leaving the profession.
The Professional Association of Teachers believes the 2 per cent rise suggested by the Government, with 2.25 per cent for those on the first point of the main scale, will not match the cost of living.
But it has chosen not to make a separate submission and says it will make its case when giving oral evidence to the review body with its RIG partners.