Sunny says the conventional ways of arguing for a more liberal immigration policy have been unsuccessful. I agree. I also agree that we shouldn't look to the Labour party to change this. Political parties tend to follow the public mood, not lead it.

So, how should we make the case for more open borders? One guide should be Jon Haidt's The Righteous Mind. He says there are six moral "taste receptors": care/harm; liberty/oppression; fairness/cheating; loyalty/betrayal; authority/subversion and sanctity/degradation. One reason why conservatives have often suceeded, he says, is that they often appeal to all six of these whereas leftists, in focusing upon care and fairness, appeal to more restricted palates. They're like chefs who only serve salt, he says.

Popular arguments for immigration, then, should try to appeal to all the receptors.

In one sense, this is easy. The case for immigration is one for freedom; people should be free to hire whom they want and live where they want. We should never stop pointing out that (some?) Ukippers' claim to be libertarian is mere hypocrisy.

In other cases, though, it's not quite so easy. I'm thinking of three receptors here.

1. Care/harm. Anti-immigrationists fear migration will harm (some) workers, and perhaps put pressure on public services. One reply to this is to tie in the case for open borders with redistributive policies to help the low-paid. Another is to reframe the debate: shouldn't we care for people who want a better life for themselves?

2. Fairness/cheating. Anti-immigrationists fears migrants will disproportionately claim benefits. To this, the answer must be the facts. And again, there's a need for reframing; what about being fair to people who want to come here and work hard?

3. Loyalty/betrayal. This is the nub. The strongest foundation for anti-immigration attitudes lies not in economics or hard facts but in an inarticulable sense that migration will change the national character. It's no accident that there's a big overlap between antipathy towards immigration and towards gay marriage; both are based upon a conservative disposition which, in many ways, is an admirable instinct.

How do we combat this? Paradoxically, we do so not by being modern metropolitan liberals, but by celebrating our "national story" - by pointing out that immigration is nothing new but part of our heritage. Churchill was the son of an immigrant, as is the heir to the throne. You don't get more British than that. And one-fifth of the pilots who fought in our "finest hour" were foreigners.In fact, the number of Poles living in the UK would have to rise by two million merely for their proportion of the UK population to equal the proportion who fought for us in the Battle of Britain. I could go on - though not perhaps this far.

Another thing we should do is celebrate immigrants' successes. If the gutter press can highlight the tiny proportion of immigrants who are benefit cheats or criminals, shouldn't we highlight the large numbers who are bring great benefits to the nation. To confine myself just to Oscar winners in recent years, we have Danny Boyle, Rachel Weisz, Helen Mirren, Daniel Day-Lewis and Tilda Swinton.

Herein, though, lies a paradox. We don't think of successful immigrants as immigrants at all, by virtue of the very fact that they have integrated so well. And nor should we. But this naturally creates a bias towards thinking of immigrants as a "problem" - simply because the countless successes aren't "immigrants". In this sense, perhaps, it's hard to argue for the benefits of immigration. But we should try.