He is at it again. Whatever the short-term political risk, David Cameron is determined to lead his party into unfamiliar territory. "Social mobility" is his latest raid behind enemy lines; he wants to turn the Tories into "a party for working people". The risks are clear. When Mr Cameron talks about social mobility, he will remind the voters that he is an old Etonian. Mr Brown's supporters will try to encourage a sceptical reaction.
Yet there is no reason why an old Etonian Tory should be embarrassed to talk about social mobility. His party has always encouraged it. Social mobility in Britain is far more common than the myths would suggest. Many observers, especially foreigners, are deceived by the survival of ancient forms and titles. Surely a society which tolerates these must be rigidly stratified? Not so: many of the holders of these apparently ancient titles are the descendants of recent money and upward mobility.
At the beginning of the last century, the five sons of a Merthyr Tydfil estate agent came to London to make their fortunes. Within 30 years, they were all peers or baronets, owning country houses, riding to hounds, belonging to White's. The Berry brothers - then owners of The Sunday Times and The Daily Telegraph, not to be confused with the wine merchants, made a lot of money and moved upwards.
According to popular mythology, aristocrats looked down on the nouveau riche. No doubt some did. But for everyone who reacted like that, another six were trying to marry them to their daughters. The British aristocracy was never a closed caste. Nor is a party which was led successfully by Ted Heath, Margaret Thatcher and John Major.
Yet even if we get the history right, there is still a problem. As the bold and the enterprising thrust their way to the glittering prizes, there may have been social mobility at the top. As society has grown richer, the middle class has expanded. But what about the bottom? There, the data lead to the grim conclusion. The economic changes associated with globalisation and the decline of heavy industry imposed redundancy on much of the old working class. Some of it moved up; a lot of the rest down - and the problem has been compounded by education.
It is often argued that the English (as opposed to the Scots) had an ambivalent attitude to education. This was said to originate in the public schools which disdained the oily-rag or counting-house vocationalism in vogue on the Continent and saw their role as producing well-rounded men who would make good imperial administrators. That was always a caricature, but such little truth as it possessed disappeared a generation ago. The public schools suddenly became alert to the growth of the knowledge economy. They knew that not many future parents would be Squire Browns, declaring that as long as young Tom grew up to be a gentleman, nothing else would matter.
Over the past few decades, the English public schools have improved dramatically, admittedly from a high base. Most of them now offer an outstanding education which explains why so many parents impoverish themselves to pay for it. But 40 years ago, just when the public schools were preparing for educational overdrive, a lobotomised version of the old public school ethos infected many comprehensives. They saw their task, not as narrow education in the sense of making their pupils learn things, but as encouraging the well-rounded, well-balanced citizens of an egalitarian Britain.
The public schools were preparing their pupils to compete. Many comprehensives were preparing well-rounded unemployables: children who were well-balanced - innumerate and illiterate. In the absence of Stalinist egalitarianism, those children were stuck at the bottom. Such comprehensive schools were the enemies of social mobility.
Throughout India, China, the rest of the Far East and Eastern Europe - all the competitor countries who want our jobs - there is a hunger for learning. So a radical improvement in British education is not just necessary to promote social mobility. It is a vital economic priority.
There is, of course, an easy option. It appears to address the problem and it would help the Tories' electoral prospects. The movement to comprehensives destroyed most of the grammar schools which once offered a good education to children from poor backgrounds. It would be simple for a Tory leader to call for the return of grammar schools in the name of social mobility, thus cheering up the hard-pressed Tory lower-middle classes who cannot afford private education. They would all assume that their children would go to grammar schools.
But the grammar schools only educated around a quarter of the population, one reason why the Tories of the 60s and 70s - including Mrs Thatcher - did not defend them. You do not win elections with a quarter of the vote.
Nor do you win economic success with a quarter of the population. That explains the stance David Cameron has taken. Old-fashioned Tories who fear that he is once again departing from orthodoxy should reassure themselves. In reality, he is preaching pure Thatcherism. She did not protect the grammar schools. She gave enormous help to working families by selling them their council houses - and she was the Tory who first used the phrase "classless society''.
Like Margaret Thatcher, Mr Cameron believes that social mobility and a modern economy march together. So he is determined to improve education for everyone. It will be a mighty task to turn that rhetoric into reality. But David Cameron is convinced that nothing else will do.