The government has written to recently retired teachers inviting them to return to the classroom, in an attempt to tackle the teacher shortage.

As teachers' unions in London have voted to refuse to cover for staff shortages, the government says that it has written to 25,000 teachers who have retired in the past five years.

As an incentive to these former staff, they can return to teaching for two terms without losing any pension entitlement.

This was a practical attempt to cut through red-tape and get extra teachers into schools as soon as possible, said a senior government source.

The Schools Minister Estelle Morris has attacked the unions' work-to-rule plans as "wrong and can only damage the pupils".

Recruitment drives

While the unions say the government has been refusing to accept the scale of the teacher shortage, the schools minister says that there are signs that recruitment initiatives are working.

"There are almost 2,300 more people training to be teachers now than a year ago, the majority of whom will qualify this summer and be available to teach this autumn," said Ms Morris.

"Teacher numbers in England were nearly 7,000 higher in January 2000 than they were two years ago, and recruitment to initial teacher training has risen for the first time in eight years," she said.

The minister also highlighted the reforms of teachers' pay, including performance related pay, which would make teaching a better-rewarded career.

In a reply to a parliamentary question, the government has said that the average teachers' salary would have increased by more than 10% compared with last year - up to �27,900.

There was also a "starter home initiative" to help teachers with high housing costs and an increased package of financial incentives for students to enter teacher training.