My middle-class fears about state secondaries, by Clegg

The Liberal Democrat leadership contender, who went to Westminster School, said he shared the concern of "aspirant parents" in the capital.

Mr Clegg, who is favourite to replace Sir Menzies Campbell, said he wanted to see his children taught in the state sector but refused to give a commitment that they would not be schooled privately once they reached secondary age.

He and his wife Miriam have two boys aged three and five who are at a state primary in south-west London. Like many middle-class parents, Mr Clegg said he faced the "psychological problem" of taking children from a "nurturing, child-friendly" primary to a "factory-scale secondary school".

He told the Evening Standard: "That's the crisis in London. The middle classes are leaving the state sector in droves."

Mr Clegg said this was partly because they think their children will be mixing with children who will not help their child reach their full potential. He said: "I want to educate my children in the state sector but I am not going to start making commitments about decisions that affect my children."

Signalling that he intends to take on the Conservatives over education reform, Mr Clegg said there was a "real problem" with the quality of secondary education in London and that parents faced "a cliff edge at 11 far worse than in other parts of the country".

He continued: "Do I, as someone who knows a bit about the London education system, feel there's a real problem for aspirant parents in finding an education which they think is right for their kids in the secondary sector? Yes, you see it - a massive flight to the private, fee-paying sector at that point.

"Do I want to avoid that for my own children and for thousands of other children in London? Of course I do. Am I going to make commitments about what I do with my children's education? Absolutely not. I am a parent before I am a politician."

His solution is to target extra funding - as much as £2.5 million - at the hardcore of under-achievers who are holding back other children as well as failing to achieve acceptable standards for themselves.

"The great crisis in the English education system is you have a tail of grotesque underachievement.

"There are about 15 to 20 per cent of kids who are coming out barely literate or numerate and, most important, where social progress doesn't seem to be boosted by the education system at all."

Mr Clegg also expressed his frustration with leadership contender Chris Huhne for the personal tone of the contest. Still smarting from being called "Calamity Clegg" by an aide to Mr Huhne, he said he had found the past weeks "neither fruitful or enjoyable", adding: "I accept the tenor of the debate has been extraordinarily introverted and would have been almost entirely incomprehensible to large parts of the public."

He said the parliamentary party has been "inward looking and caught up in a series of ructions in the past couple of years", adding: "I don't think a party bobbing around at 11 to 18 per cent of the vote, having had those problems, can afford to be inward looking. We can't carry on testing the patience of the public."

Despite being of the same generation as Tory leader David Cameron and sharing a similar background, he said differences between them were greater than the similarities. "We are the same generation, so he like me was aware of the politics of the late Seventies and early Eighties, but we had completely different reactions."