Charles Clarke is coming under pressure to change rules which ban experienced private school teachers from entering the state system.

Tristram Jones-Parry is retiring as head master of Westminster School and wants to "give a bit back" in a state school.

But he is effectively disqualified because he does not have a state-recognised teaching qualification.

Professor Celia Hoyles, the chief adviser for mathematics, said she wanted a rule change that would allow up to 5,000 independent school teachers to move into state schools "on a case by case basis".