A Tory think tank claimed yesterday that top teachers could earn up to £70,000 as it tried to whip up support for performance-related pay.

Policy Exchange said some teachers could expect to reach the salary without leaving the classroom within five to eight years.

Its paper insisted performance-related pay would attract the best graduates and not be used to hold down pay for the majority of teachers.

Head of education Jonathan Simmons said: "We want schools to have the flexibility to reward and retain their best teachers and to use them to improve outcomes for young people."

But Mr Simmons has previously worked on Con-Dem government education strategy and co-founded the Greenwich Free School.

He also penned the coalition's "Open Public Services" white paper which called for services to be handed to privateers on a payment-by-results basis.

And the Policy Exchange's latest report was labelled "flawed and disingenuous" by ATL teaching union leader Mary Bousted.

She said: "Performance-related pay risks damaging children's education by putting off the best and brightest students from becoming teachers and demotivating current teachers.

"It has nothing to do with improving children's education but everything to do with saving money."

Scrapping national pay bargaining for teachers in England and handing power over salaries to headteachers is a key policy of Education Secretary Michael Gove (left).

A Department for Education spokesman praised the Policy Exchange report.