The National College for School Leadership in Nottingham says half of heads will retire over the next decade with no policy for replacing them.

Researchers say campaigns have addressed a shortage of new teachers, but there needs to be a concentrated effort on training up future leaders.

They say potential head teachers need to be identified and prepared.

We've got a good generation of young teachers, we've got a good crop of deputy heads, we just need to make sure they are ready Geoff Southworth, director of research

In this way separate schools and education authorities have treated the employment process as an individual problem.

Instead, the college suggests the situation would be improved if leadership and talent was spotted at an early stage.

Geoff Southworth, director of research at the college said: "It is the schools along with others that need to be preparing tomorrow's school leaders.

"We've got this ticking time bomb where a lot of teachers are now going to leave the profession as a larger than average number of head teachers and deputy heads are over 50.

"When that generation go, it's a large group and they need a larger than average cohort of deputy heads and other school leaders ready to take over from them.

"What we need to be doing is what many schools have always done which is prepare people to move into leadership.

"We need a larger group of schools to be doing that.

"We've got a good generation of young teachers, we've got a good crop of deputy heads we just need to make sure they are ready."

The college was set up in Nottingham four years ago.

The issue will be discussed at a conference on Thursday attended by the Education Secretary Charles Clarke.