I have size ten feet. This is a biological fact which I cannot change. In some contexts, it's of utmost importance, such as in a shoe shop. In other contexts, though, it's irrelevant.

This might sound utterly trivial. But it's why I agree with Phil that David Goodhart's talk of "legitimate ethnic interest" exudes "moral foulness."

The thing is, we all have multiple identities: I'm tall, white, Oxford-educated, bald, heterosexual, male, bourgeois with a working class background, an economist, an atheist with a Methodist upbringing. And so on and on. The question is not: what are my identities? But rather: which of these identities matter? Amartya Sen has written:

A Hutu labourer from Kigali may be pressured to see himself only as a Hutu and incited to kill Tutsis, and yet he is not only a Hutu, but also a Kigalian, a Rwandan, an African, a labourer and a human being. Along with the recognition of the plurality of our identities and their diverse implications, there is a critically important need to see the role of choice in determining the cogency and relevance of particular identities which are inescapably diverse. (Identity and Violence, p4)

Even if you accept biological essentialism, the question of which of our multiple identities becomes salient is surely in large part a social construct. In Sen's example, it took propaganda and pressure to raise the prominence of Hutu identity to genocidal importance. In the UK today, there's a prominent identity divide between Leavers and Remainers, but this was much less significant a few years ago.

Not only does biology not suffice to determine the salience of identities, nor even does economics. For example, tall people earn more than short ones and good-looking people more than ugly ones, but politics isn't divided along these lines. The converse is also the case; the isn't much economic difference between the English and Scots, but there is a political difference.

Marxists have long been aware of this. We believe the working class has distinct economic interests. But the job of getting them to see this - of building class consciousness - is a tough one. Such awareness requires industrial and political action.

Which brings me to my beef with Goodhart's piece. No good can come from raising the salience of racial or ethnic identities. I say so for four reasons:

- It's not obvious that I have much common interest with (say) an unskilled 20-year-old - which of course is not to say our interests necessarily conflict. Attempts to identify us as a common group will generally involve distinguishing us from other ethnic groups. I see no upside in this, and plenty of downside.

- If we must think in racial terms, whites are the predominant group in the UK: yes, we should ignore the bleating of some imbecile rightists. Asking a dominant group to assert its self-interest will increase inequality and domination.

- One of the easiest ways people have of conning themselves is to come to think that their interests are morally legitimate. Slaver-owners, for example, found it very easy to persuade themselves that slavery was justified by blacks' supposed inferiority. Inviting white people to pursue their interests almost inevitably means inviting them to believe in their moral superiority. This must of course be rejected.

- Salience is a zero-sum game. If ethnic divisions become more salient, others thus become less so. Not least of these divisions is that between rich and poor. The politics of ethnicity thus serves, in practice, to defend and widen class inequalities. As LBJ said: "if you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket."

My point here is so simple and obvious that I'm embarrassed to say it. We're all different in all kinds of ways. Which of these differences matter, and by how much, is a social construct. Ideally, ethnic differences would matter no more than differences in shoe size. Any attempt to raise their significance moves us away from this ideal and is thus regressive.