Politicians and pundits have been predicting the collapse of independent schools since the end of the last war, if not before. Perhaps 30 years or so ago, with a Labour party red in tooth and claw (when it was in opposition, at least) they had good reason to believe it.

Since then, the independent schools have gone from strength to strength. From the demise of direct grant schools to Thatcher’s social revolution, which enfranchised a new generation of school fee-payers, they have flourished. Now, however, with no obvious threat on the skyline, I believe the independents are in danger of being caught off-guard.

I am not referring here to the economic issue, though such schools cannot indefinitely raise their fees without demand for places tailing off, as appears to have already occurred on the boarding side. Nor do I foresee any development of moral revulsion against independent schools, but remain surprised at how tolerant the British public is to the obvious inequity their existence continues to bring.

Independent schools have traditionally drawn their strength and forged their identity from being different, not only from the state sector, but within themselves. Thus they have offered a genuine choice to parents. Now there appears to be an unstoppable trend, driven largely by market forces, towards a homogeneity that threatens to undermine the independent schools’ most compelling justification to exist.

There has been a steady development towards the removal of variety and choice within the independent sector itself. The sternest critics of single-sex or boarding schools would surely not dispute that the opportunity should at least be there for parents to choose between them and co-educational andor day schools. By the year, the choice is becoming more restricted.

But it has been the emphasis and priority given to academic results which has most effectively eroded distinctions within the sector. While independent schools will continue partly to justify their existence on the grounds that they set high academic standards, they have come up against the problem that this may not correspond, and perhaps even may conflict, with the priority they must now give to ensure a high position in the league tables.

The now national obsession with exam results is doubly unfortunate for independent schools, for it has been responsible not only for removing the differences between them, but also between independent schools as a whole and their rivals in the state system. The horns of the two sectors are now locked and the battle is being fought for the same prize. There is no guarantee that independent schools will emerge victorious.

A glance at the notorious league tables would seem to confirm this. Independent schools’ domination of the top positions has, at least until recently, been maintained because they have had more resources to achieve good exam results, but also because they have been able to be more selective in their intake. While the first advantage may still hold, the second has been undermined by the pressing need to fill places at any price.

Conversely, selection has come back into fashion in the state sector, and its adoption does not appear to be confined to the Conservative party. The emergence of the grant-maintained schools has not only accentuated the problem of recruitment for independent schools, but seriously challenged the assumption that they offer the best education, if quality continues to be measured by league table position. The recent success of the new state sector elite in breaking into the premier league has forced a reappraisal of the old assumption that independent schools, almost by definition, offer the best education.

The next generation of parents will therefore be asking “Why spend Pounds 10,000 a year on school fees when a similar education, with the same results, can be experienced at the local grammar for nothing?” A fair question.

The problem for the independent schools is that they have, until recently, built their raison d’etre, at least in part, on values that no league table, value-added or not, can assess. How does one measure esprit de corps, or self-reliance, or the value of a “rounded education” that provides the opportunity for an individual’s potential to be tapped - a potential which may be displayed in the school concert hall or on the sports field as much as, or even instead of, in the classroom?

Such an education, already perhaps regarded as rather quaint and old-fashioned, is at present being sacrificed on the league table altar. One does not have to work in the independent sector to know that extra-curricular activities no longer have the place they used to, especially if they have to grind to a halt for most of the summer term to give way to preparation for and the sitting of modular exams.

If the independent schools’ future is to be secured they will to have to sacrifice their market’s short-term demands for a longer term strategy for survival. This might involve a redefining of their identity and the use of their extra resources to offer, once more, something distinctively different, in process and product, from their rivals in the state sector. An adherence to educational principle rather than a response to what is immediately expedient would be a precondition. In the long term the market, fickle though it is, may start to look for an alternative dish to the blancmange served up by the vast majority.

The great educational changes of the last 200 years were not introduced on the basis of customer demand. How many youngsters, for example, wanted to go to school when an Act of 1880 made attendance compulsory? Yet who now would advocate its repeal? For the security of their own future as much as for the cause of education, it is time for independent schools similarly to buck the market, and put education above economics and principle above popularity.

Graham Lacey is head of careers at Sevenoaks School