Why is Gordon Brown emerging as the Labour champion of remaining in the EU? There are both short answers and long answers.

The short one is panic in the ranks of the pro-EU campaign, as polls appear to show the Brexit option surging ahead in the polls. David Cameron and George Osborne's onslaught of economic warnings appears not to have the traction they had hoped.

In an increasingly uncertain referendum, the choices of Labour voters could be crucial as they decide whether to back the official party position of Remain, or Leave, or simply register their indifference by staying at home.

And when panic is setting in, you turn to Gordon Brown. Sometime saviour of the world's economy, the lone cavalier who rode to the rescue of the No campaign in the independence referendum. Is enough of his magic left to help Remain squeeze over the line in next week's vote?

The longer, and slightly less facetious answer is that Labour has been largely invisible in the Remain campaign, with a Loughborough University study finding Labour voices present in less than 4% of TV coverage and just 8% of print coverage of the EU Referendum.

In Scotland Kezia Dugdale has not been prominent, but this matters less with support for staying in the EU apparently still holding up north of the border (and because Labour's reliable vote here is much diminished in any case).

But south of the border Jeremy Corbyn expressed ambivalence when choosing to rate his support for remaining in the EU as, at most, seven and a half out of ten. How can the party faithful be rallied to support the EU, when Labour's leader is so lukewarm?

This could be seen as the new honesty in politics which he espoused in his leadership campaign. But that is not the aspect needed. Mr Corbyn needed instead to marshal the excitement among young voters which his leadership campaign rode to victory. He needs to give supporters a lead on how to vote and a reason to get out and do so.

It is hard to see how he can go from half-hearted to full-blooded in the remaining days.

So Labour Remain leader Alan Johnson has turned to Gordon Brown more in hope than expectation.

Mr Brown can point to the impact of the latest polls on sterling as a warning of what is at stake, and has rightly pointed out that Labour supporters may have more to lose from turning their backs on the EUs social and employment protections.

But that will not be enough. Remain needs to come up with credible answers on immigration to address the strength of feeling, particularly among working class voters, about the effect on jobs and wages of free movement within the EU.

Mr Brown could also counter the kind of opportunism that led Brexit supporter Michael Gove's to suggest Scotland will be given control of its own immigration by Westminster following a Leave vote.

But he doesn't seem inclined to do so, and if the Remain campaign as a whole cannot reassure the public on this, it increasingly looks as if our time in the EU may be drawing to a close.