Primary heads' posts on both sides of the border attract only around five applicants, according to separate surveys in Scotland and England.
Scottish authorities admit they have a problem and share with headteachers'
associations rising concern about the low numbers of applicants. They pinpoint the recent job-sizing exercise on deputes' and heads' posts, the perceived isolation of headship and the high degree of public accountability and exposure.
Mandatory training for headteachers through the Scottish Qualification for Headship may also be restricting the number of candidates, some teachers and authorities believe.
The Association of Head Teachers in Scotland says that many aspiring primary heads often end up staying put as deputes because of confused promotion structures.
Senior posts which carry salaries of pound;40,000-pound;50,000 are attracting an average of 5.4 applicants, its recruitment analysis confirms.
The AHTS survey of authorities reveals that the number of vacant posts for primary posts has risen by nearly 60 per cent in the past year, from 70 to 110. The previous three years had shown a fairly static picture.
"This is a colossal increase," Greg Dempster, the association's general secretary, said.
A survey south of the border reveals a similar trend with one in five schools failing to find a suitable candidate. Primary posts attract only five applicants and nearly 28 per cent of primary head vacancies are unfilled. In secondaries, the figure is 20 per cent.
The survey was commissioned by the National Association of Head Teachers and the Secondary Heads Association.
In Scotland, the AHTS is pressing for a review of the job-sizing toolkit which it blames for confusing the career structure facing promoted staff in primaries. Deputes in some schools can earn more than heads in neighbouring primaries, a situation it believes is also damaging career paths in special schools.
Mr Dempster said that the largest primary in Glasgow managed to attract only four candidates when it advertised recently. Only South Lanarkshire seems to be exempt from the recruitment crisis. "It is unusual in that out of 32 vacancies filled, there were generally high numbers of applications and no readvertisements," he said.
"We think that job-sizing and the confusion that it has created in management structures has made a significant contribution to the drop in applications, although it is not the sole factor. If job-sizing is not revisited, the situation is going to get worse."
The AHTS wants a clear promotion structure where heads are paid more than deputes and where responsibilities are fully recognised. But so far the national job-sizing toolkit has remained a closed secret. The association wants to see any review begin by next summer.
Ewan Aitken, education spokesman for the local authorities, refuted the association's allegations. "It is too easy to blame job-sizing," Mr Aitken said. "Across the board, people say that teachers are moving less than they used to and factors like house prices affect people's decisions. There are a number of aspects to this."
In England, John Dunford, SHA general secretary, said people were put off applying for headships by the range of responsibilities, over-accountability and the pace of school reform.