One of the stranger poll findings of recent days has come from ICM. It asked voters "which team do you think is better able to manage the economy properly?" It found that 53% said May and Hammond against only 15% saying Corbyn and McDonnell. Only 16% said they didn't know.

This is odd because it cannot be based upon hard facts. So far, all we have from May on the economy are words. And these bear the same relationship to McDonnell's as Melania Trump's did to Michelle Obama's. In abandoning Osborne's target of a budget surplus, and demanding worker-directors, more housebuilding, more infrastructure spending and an activist industrial policy, Ms May has appropriated McDonnell's ideas.

This poses the question: why, then, is she so much more trusted on the economy than McDonnell, when so many of her new ideas are his?

It could be, of course, that voters know something we don't. One big fact, however, suggests this is unlikely: millions of people are financially illiterate. For example, economists at the University of Nottingham asked mortgage-holders: "Suppose you owe £100,000 on a mortgage at an Annual Percentage Rate of 5%. If you didn't make any payments on this mortgage how much would you owe in total after five years?" Only 51% gave the correct answer, of over £125,000.

If people don't know basic economics, why should we assume that they are good judges of economic policy?

Instead, there's another possible explanation here. You'll not be surprised that I suspect it lies in cognitive biases.

One is wishful thinking; people just hope that a popularish new Prime Minister will be competent.

Another is a form of halo effect: Labour now looks more disorganized than the Tories, and this contaminates voters' assessments of economic policy.

And then there's an incumbency advantage. Simply being in office gives one gravitas and respect.

This biases might be magnified by our biased media, but I fear they might exist even if our media were not beneath contempt.

But might there be something else - the power of brand? Years ago, the Tories succeeded in presenting themselves as being "stronger" in the economy. This is partly because of memories of the inflation and "winter of discontent" under the 1974-79 Labour government, and partly because they were the party of business and voters (and the media) think that what's good for business is good for the economy.

Of course, the latter perception should have been destroyed by the fact that austerity and Brexit (two related things) have been bad for business. But it seems not to have been. This could be because May and Hammond are regarded as clean skins, untainted by the failures of the predecessors. It could also be because are ideas are shaped in our formative years. The ICM found that May and Hammond's lead on the economy was even greater among over-65s - those who have livelier memories of the inflation of the 70s and the Tories' more successful attempts to align themselves with business interests.

It could be, therefore, that the Tories' lead on the economy for the same reason in part that they are still so unpopular with ethnic minorities: voters' perceptions are shaped not just by current facts, but historical ones. We know that peoples' attitudes to risks are shaped (pdf) by events years ago: why shouldn't their political attitudes also be so influenced?

My point here is a depressing one for all Labour supporters. It's that winning "credibility" on the economy is a massively uphill task. Yes, Blair succeeded in this - but he was massively helped by "Black Wednesday", and voters have since reverted to the default perception that it is the Tories who are to be trusted on the economy.

In theory, the coming economic slowdown might help Labour fight this, as "Black Wednesday" helped it. How to capitalize fully upon this, however, is a trickier matter.