Daniel Hannan is an MEP for South-East England, and a journalist, author and broadcaster. His most recent book is What Next: How to Get the Best from Brexit.

Suppose I were to tell you that Labour’s promises would cost £50 billion. How would you feel about it? My guess is that, if you’re a Labour supporter, you’ll assume that that money can easily be squeezed from the undeserving rich, tax-dodging corporations and the like. If, on the other hand, you are not a Labour supporter, you’ll believe that that figure will mean higher taxes in general, a less competitive economy and slower growth.

Now suppose that, instead of £50 billion, the figure were £100 billion. How many people would shift from the first column to the second? My guess is almost none. Numbers on that scale simply make no sense to most of us. Our brains are designed to deal with practical rather than abstract questions. We can imagine what we’d do with £100 or £1,000. But £100 billion?

So we instead go with our hunches. Do we like and trust the people making the proposal? If we do, we are likely to give them the benefit of the doubt. If we don’t, we won’t. That would be true, in most cases, even if the figure were a trillion pounds – which is just as well for Labour, since that number comes closest to their actual spending plans.

Labour strategists are banking on our general innumeracy. I don’t say that they are taking us for fools. Plenty of clever and educated people can’t process numbers on that scale. It’s why charity appeals tell individual stories rather than offering figures. It’s why, as Stalin is supposed to have said, one death is a tragedy, but a million is a statistic.

Most people are partisan. Most, though they don’t like to admit it, begin with their preferred conclusions. When Barack Obama ran up a large deficit, Tea Party protesters took to the streets in every state demanding a return to fiscal balance. When Donald Trump maintained – or, on some measures, increased – that deficit, the Tea Partiers stayed at home. Why? Because people are wired to respond to people, not abstractions. Tribal loyalties trump big numbers.

There is, however, an important qualifier. Voters who are not already partis pris will often be influenced, consciously or not, by those who intermediate the numbers – that is, by journalists, commentators and experts. If every analyst lines up to declare that a party’s figures are ridiculous, it makes a difference.

Importantly, this didn’t happen last time. There was a general assumption among pundits that Corbyn couldn’t possibly win, and that his promises were therefore to be treated as light entertainment. A similar asymmetry had benefited Trump six months earlier. He, too, was not taken seriously. His promises were placed before the electorate with a kind of amused smirk, while Hillary Clinton’s, like Theresa May’s, were properly analysed and criticised.

In consequence, there was surprisingly little discussion of the sheer unaffordability of Labour’s 2017 manifesto. Most commentators treated its absurdity as a datum or given – something that needed no elaboration. Result? Voters heard the promises (“no tuition fees!”) but not the fact that they were unfunded.

John McDonnell seems to have concluded from that experience that, if you expand the promises, you expand your support; but, since no one really gets big numbers, you won’t lose many voters on the other side. Even on his own figures, this manifesto would cost nearly twice as much as the far-Left programme he offered two-and-a-half years ago. In reality, that price tag doesn’t include the vast expense of the nationalisations, the four-day week or the loss of revenue prompted by capital flight.

How many people are bothered? Is McDonnell right that the battle-lines are unaffected by actual statistics? If the number of fiscal conservatives is fixed, after all, he might as well purchase the support of as many groups as possible – students, waspi women, benefits claimants, public sector workers.

But there is a limit. On Monday, the editor of ConHome suggested that “McDonnell might as well pledge £1 million to all comers. He could make it £1 billion while he’s at it. It would be no more or less credible than all his other plans.”

I suspect that, if he offered us each a million pounds, even committed Labour voters would smell a rat. The angriest Momentum activists, convinced that austerity is a product of greed and sadism, would surely realise that there isn’t the money to make such a pledge. So let’s ask a question. At what point do Labour’s pledges topple into obvious fantasy? When do people start listening to the independent commentators who are staring speechless at these wish-lists?

My sense is that, to the extent that we will see any outbreak of collective incredulity, we are seeing it now. Having already come up with risible spending commitments, Labour has now cheerfully added an unbelievable – a literally unbelievable – £58 billion commitment to bump the pensions of the women who lost out when the retirement age was equalised.

For what it’s worth, I have a lot of sympathy with those women. The change happened very suddenly, and many had no time to arrange their finances accordingly. But the issue is not just whether the waspi women have a point. It’s also whether we have £58 billion to spend.

How much is £58 billion? To put it in context, the savings made between 2010 and 2013, the “savage Tory cuts” that brought protesters to the streets and pushed Labour politicians into making deranged claims about people “dying from austerity”, shaved £14.3 billion from the budget. The waspi shortfall is four times that sum.

Indeed, £58 billion would be half as much again as the all the money saved through welfare reforms since 2010. Labour, which created the deficit in the first place, and then spent the following decade howling down attempts to fix it, now proposes to spend vastly more than even Gordon Brown.

Do we understand that? Do we care? We’ll find out in two weeks’ time.