Faith schools like to have their loaves and fishes, and eat them too.

When accused of fostering religious apartheid they stress that they are open to pupils of all faiths. When asked what benefits religion brings to a school, they talk about clear and strong values. But if the values a school imparts are distinctive to one religion, how can teaching them be inclusive of others? And if those values are shared by people of other faiths or none, why the need for a distinctly religious ethos in the first place?

We can see this unsustainable tension in schools such as Immingham, a Lincolnshire secondary being turned around by Stephen Carey, who is looking to turn the school into an academy with the help of the Oasis Trust, a Christian charity.

As The TES recently reported (“Christians hope to be saviours”, May 27), a key selling point is, as Mr Carey says, to “encourage Christian values such as patience and respect”. But at the same time, the school will also “be open to children of all faiths and none”.

Imagine, however, being a child of another faith or none at a school where the difference between right and wrong is explained using religious beliefs to which you don’t subscribe. “Respect” is a Christian virtue, you are told. But you are not a Christian. Does that mean you are incapable of appreciating respect as a value? Or that you needn’t respect others?

And if you are a Christian, how does that make you view others, who lack what you are taught is necessary to be truly moral? And how credible is the claim that values must be rooted in the Bible when most people come from homes where no adult reads it, goes to church or prays? Isn’t that offering a vision of ethics which is not going to stand up in the real world beyond the school gates?

Supporters of faith schools will reply that of course they are not saying that their religion has a monopoly on moral values and that is not what they teach. But if they seriously thought that, what they should teach is not that their values are distinctly religious at all, but that they are shared by good people of all faiths and none. And why are they so shared? Because they are secular values first, and religious values second.

By “secular” we do not mean “atheist”. Secular values are those that do not require the support of specific religious dogmas. As a result, they are values all thinking, decent people can share.

All the important values are secular: respect for human rights, considering the social consequences of our actions and so on. The only purely religious values are those that concern scripturally-derived rules for prayers, fasting, diet, clothing, marriage and so on. No one, I think, believes state schools should tell pupils that these are core values they should hold. If any did, their claims to be inclusive would be utterly hollow.

By teaching only secular values, and their secular basis, schools can show students that there is a common morality we can share, even in a multi-faith world. It also shows children that ethics is not just for the religious. But by teaching religious values, schools can only help create the impression that values are what divide us, and that without strong religious belief, morality is impossible. In a country where few are religious, that is a dangerous message.

I accept that for people such as Mr Carey, values such as respect are intimately linked to their faith. And I also understand that religion provides much of their motivation for wanting to help children in difficult areas. But when it comes to teaching values, they must base their teachings not in what is distinctive to their faiths, but what is shared by all of decent society.

Julian Baggini (www.julianbaggini.com) is editor of The Philosophers’

Magazine and author of The Pig That Wants To Be Eaten and 99 other thought experiments (Granta).