The charitable status of the 2,500 independent schools in Britain is a touchstone issue on the political Left. If private schools themselves cannot be abolished, then at least their status as charities can be withdrawn. In sum, designation as a charity is worth £100 million in tax relief and, until the Charities Act 2006 required all charities to show they provide a public benefit, such status was automatic for most independent schools.

In 2007 the Charity Commissioners clarified the criteria for charitable status. Schools must show an identifiable public benefit and their services must be available to the poor. It is easy to see that they satisfy the first of those criteria but less obvious that they satisfy the second. That is why independent schools have been offering bursaries and sharing their facilities with state schools. This has not been enough to satisfy the Charity Commissioners. In the first batch of five schools surveyed according to the new criteria, two have failed because they were unable to offer enough bursaries to children whose parents could not afford the fees.

It is easy to construct an argument to say that independent schools — which have travelled a long way from their origins as places for male scholars from poor backgrounds — are not especially worthy recipients of a tax advantage designed to meet a pressing social need. That said, it is very hard to see what problem it solves to strip them of charitable status. Some of the smaller private schools might struggle to survive. Fees at the larger schools would rise to pay for more bursaries meaning that, apart from the assisted few, the best private schools would become even more the exclusive preserve of the wealthy clever than they are now.

In fact, the argument about charitable status is a sideshow. Independent schools could more effectively meet the charitable objective of contributing to public benefit by continuing the quest that some of their number have embarked upon, namely to become needs-blind as quickly as possible. This would mean that they build a sufficiently large foundation to ensure that all places are open to all, subject to a means test. Any child, irrespective of parental background, would be guaranteed a place. The best independent schools would then become genuinely meritocratic institutions, with clear public benefits.

At the moment, the choice between the public and the private sector is a chasm. The options are the state school or saying goodbye to a fortune. There are a few schools offering a private education for £3,000 per annum but not enough.

At the same time, the whole school landscape could change fundamentally in the event of a successful Conservative government. A system comprised mainly of independent state and voluntary-aided schools, some run by companies in chains of schools, would alter this calculation. That means new providers, offering new school places. It means getting round restrictive planning regulations. It would also make sense to allow companies to turn a profit in schools. It is unlikely that enough new school places will be created purely from the voluntary sector.

Schools reform is at an exciting stage. If this were the school landscape — a vibrant private market serving all income groups — then any further time spent on this small matter of £100 million in tax relief looks either eccentric or chippy.