It's hard to imagine a tougher argument to make in Britain in 2016 than standing up for immigrants. The Brexit vote has seen Labour MPs have a panic attack over their constituents' views on the issue. Their response has been depressingly predictable, with many calling for an end to freedom of movement. For a party which has utterly failed to scrutinise the Tories over the summer, you can forgive yourself a moment of despair when they suddenly start doing so from the right.

This reached a grubby nadir yesterday when Rachel Reeves victim blamed Polish people who'd been attacked in the wake of the Brexit vote. Other MPs, like Stephen Kinnock, are also pushing for Labour to scrap freedom of movement.

So Jeremy Corbyn deserves huge praise for being prepared to stand up for his conference speech today and make the case for immigration. His team have made clear they won't call for an end to freedom of movement, despite intense pressure on them to do so.

It is a lonely, unpopular position. All the bravest ones always are. The little Englanders of the anti-immigration movement always celebrate as 'brave' those who speak out against it, even though nearly everyone in politics now holds this position. But no matter: Ukip campaigners are 'brave', Daily Express columnists are 'brave', Labour MPs are 'brave'. They're all so terribly brave saying exactly the same things as everyone else. Refuse to do this and you are branded elitist and out of touch.

Corbyn is standing up for the old Bennite position on immigration: If capital is allowed to cross national borders, why can't labour? Holding the labour force in place while allowing money to move freely puts workers at the mercy of management's whims.

But Corbyn's argument isn't just correct ideologically. It is also the right stance to take politically. Firming up parliamentary support for freedom of movement makes it more likely Britain can secure a deal with Europe that will retain membership of the single market. That will mitigate against the disastrous effects, predominantly on manufacturing workers, which would come from a hard Brexit.

It was particularly brave for Corbyn to refuse to say that immigration was too high. This is the point at which so many Labour MPs make a mockery of their own stance. They know immigration isn't too high and that in fact a significant reduction would inflate our debt-to-GDP ratio. They know we need working age adults to fund public services for an aging population. But they don't have the guts to say so.

So instead you get Kinnock saying 'social and political' concerns need to be addressed. In other words: 'This thing is good and we are going to make sure there's less of it.' It makes no sense on its own terms. And the public - whether pro or anti-immigration - can smell it.

But it's not enough for Corbyn to just celebrate immigration. He needs a clear firm plan and he needs a way to placate Labour voters' anxiety on the issue.

It's troubling that his team are briefing that single market membership is not an option, while shadow chancellor John McDonnell said freedom of movement was a requirement of "access". Neither of these things are true. Single market membership is on the table and it's membership - not access - which requires freedom of movement.

In getting this stuff wrong, Labour is doing no worse than the government, which barely seems to understand simple concepts related to Brexit itself. But it is not enough to be no worse than the government. Corbyn and McDonnell can't hold the Conservatives to account on the Brexit deal if they don't understand the terms they're using.

It's also a real problem that Corbyn was unable to say how much money his proposed migrant impact fund would need. Neither could he say which areas would receive the funds in order to reduce the strain on public services. He urgently needs details on policies like this. Immigration supporters are often portrayed as bleeding heart fantasists - which is ironic, given that their views usually follow from hard-headed economic analysis. But regardless, that's the impression, and by not having details Corbyn is playing into it.

He also needs to say more to reassure voters about the kind of immigration we get. This is not as perplexing a puzzle as it might first appear. Freedom of movement is not an uninhibited right. You have to be able to demonstrate that you have a reasonable expectation of a job when you move, as a recent German case demonstrated. He could cite work here as evidence that Labour can push to make sure people are not just coming to the UK to claim benefits.

Corbyn rested his immigration case on improving pay and conditions in Europe, which is a fantasy policy. It's a lovely thought, but that's really all it is. Instead, he should be highlighting how the European Court of Justice kept making judgements which gave global businesses the ability to reduce standards and wages using single market rules and laying out an agenda to change the system.

The Labour leader is not good on details and he often prizes warm sentiment over concrete plans. He needs to tighten this agenda up or else his bravery will be translated as weakness. But regardless of where he stumbled, it takes guts to stand firm on immigration. Corbyn deserves considerable praise.

Ian Dunt is editor of Politics.co.uk

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.