Increases in school budgets are being used to lure staff from their neighbours, contributing to a "chronic lack of stability" in classrooms across the country, according to a leading expert on teacher recruitment.
In a report published today, Professor Alan Smithers warns that headteachers are cutting spending on books and equipment in an effort to attract and retain teachers in the face of continuing staff shortages.
The Reality of School Staffing by Professor Smithers, Pamela Robinson and Louise Tracey of Liverpool University says that both primary and secondary schools are suffering, but primaries face particular difficulties in recruiting experienced staff.
Some heads are being forced to beg teachers not to leave for fear that they will be unable to find suitable replacements. One head from the North-east told researchers: "We have been trying to get a physics teacher for a couple of years and this year we finally got one by poaching from a neighbouring school. I have had to pay top-whack to get him and it is putting pressure on the school budget, but he is absolutely excellent."
Next week, the Organisation for Economic Co-operation and Development will publish a report stressing the importance of "an adequate supply of good quality teachers" to a country's education system.
Professor Smithers told The TES that government plans to give schools with good results greater freedom over how they pay teachers could make matters worse for struggling schools.
"Most schools are suffering to some extent but there are clearly great differences. If you are going to increase the differences between schools and there are not enough teachers then you are going to increase the disadvantages that some face," he said.
The report was commissioned by the National Union of Teachers and is part of its evidence to the School Teachers' Review Body.
It criticises the Government for attempting to hide the true extent of recruitment problems and says that more teachers rather than an increase in classroom assistants is key to tackling workload and discipline problems.
London and the South-east are suffering the worst problems but schools in all areas are affected with many forced to put staff in roles for which they are not qualified or employ temporary and overseas teachers.
Nationwide, one fifth of teachers do not have qualifications in the subject they are teaching.
Figures compiled by the National Association of Head Teachers show London schools are being charged between pound;160 and pound;170 a day for supply cover (a rise of pound;10 a day on last year) and in some cases nearly pound;200.
Many schools are paying up to pound;40,000 a year for agency staff, on top of their usual staffing budget, and one south London primary is spending more than pound;500,000. Yet many heads do not feel they are getting value for money from the agencies they use - mainly Protocol, TimePlan, Capita, Select and Teaching Personnel - a charge disputed by the agencies.
Only a quarter were confident that the supply staff provided would have qualified-teacher status and less than a quarter were confident they would be familiar with national curriculum requirements.
The news comes as London schools minister Stephen Twigg considers funding cheaper bus, train and tube fares for teachers, in a bid to keep them working in the capital.
Ralph Tabberer, chief executive of the Teacher Training Agency, told The TES that London universities could also get more cash for training teachers, in recognition of the additional costs of running courses in the city.
But there is no prospect of a London weighting increase in the pound;6,000 training bursary given to postgraduate student teachers.