The report advocates 'opening up' private school places

Mr Johnson, MP for Kingston Upon Hull West and Hessle, admitted it was an unusual step but argued that he was "not fighting a class war".

He told London's Evening Standard the boy's mother had asked for his help.

He said: "I don't think it is betraying the human race to send your child to a private school."

In an interview with the paper, he said there were no local secondary schools which had teaching to match the boy's aptitude.

'End of a chance'

"I had a single mother come to me in Hull and ask that I write a supporting letter because the private school she wanted her son to go to, and which had accepted him, had run out of bursaries.

"She couldn't possibly afford it. It would have been the end of a chance for him. She just doesn't have a suitable school close at hand and he is a very bright boy who wants to do science."

He added: "But I do believe we have to want the state sector to be as good or even better. That's why our reforms are worthwhile.

"In boroughs like Hackney, people are moving to try to send their children to the academies. If we can get that social mix where both poorer families and the better-off want to be in state schools then that really is progress.

"All the new freedoms the trust school legislation opens up will really help that."

'High quality'

He also praised the "fantastic" maths and science teachers in the private sector, suggesting they could be "borrowed" by state schools.

General secretary of the National Union of Teachers Steve Sinnott said: "Alan Johnson is relatively new to the post of education secretary.

"I would happily take him round the thousands of state secondary schools and let him meet their very high-quality maths and science teachers.

"When he has been longer in the job his views will have changed."

Mr Johnson also told the paper that he had no "fixation" with the government's target to get 50% of 18 to 30-year-olds into university by 2010.

Shadow education secretary David Willetts responded: "Alan Johnson as a constituency MP is perfectly entitled to help someone get to private school. But in that case why is he also threatening to tax private schools?

"Instead he should be trying to improve co-operation between private and state schools so that every pupil benefits."