When I lived round the corner from a "convenience" store cash machine, I used to hate the brass neck of that final question: "This machine will charge you £1.75 for your transaction. Would you like to proceed?" And then a simple "yes" or "no", when what I wanted to say was, "I don't have much choice, do I?" or "Yes, but how you live with yourself, you robot rip-off, is another question."

About 300,000 people in low-income areas don't live within 1km of a free cashpoint. This has been highlighted as a scandal for the consumer banking industry that makes "Wonga look like Santa Claus", according to Frank Field, Labour MP and government adviser on poverty.

It is, when you look at it closely, a powerful constellation of disadvantage that a) the 7 million people who make most of their payments in cash are predominantly poor, unemployed or disabled, b) the cash machines that charge are mainly located in poor areas, and c) the poor are more likely to withdraw cash in smaller sums, by necessity not by some quirk of taste, and could therefore be paying £1.75 on every tenner. Field is right to point out that this is a rip-off, and right to call for more regulation.

But it should be noted that this is merely part of a pattern; it even has a name, The Poor Pay More, and has been an observable sociological pattern since 1967, when it was systematised by sociologist David Caplovitz. You can see it in the £2 courgettes from those same convenience stores, in the unit price of energy for those paying on a meter, in the astonishing fact that the poorest decile pays the most tax ("you're talking about marginal tax rates", people always say soothingly, at this point; as though that would be ok, to have people who earn the least paying the greatest penalty for working. But anyway, that's incorrect: the boost to VAT, coupled with the senseless reduction in council tax credit, has left the poorest spending an eye-popping 47% of their income back to the government, a proportion which is only echoed in the top decile who, of course, have a surfeit of options to get round it).

And there's the point – where you have no options, you get ripped off. It is in the nature of the market dynamic that the buyer's power resides in two places: first, not especially wanting the product, and second, being able to go elsewhere for it.

When your need is high and your options are few, you are essentially going to the table not just with a poor hand, but the wrong number of cards; you're going to get fleeced.

I agree, in a mild, broad sort of way, with holding businesses to account; I do not buy into this post-Apprentice landscape in which morals are portrayed as a quirky add-on, irrelevant to the living of life. Field is basically trying to turn this into a little-guy-against-the-bully-boy narrative, in which he or some other lawmaker can step in on the little guy's behalf. That's great, regulation is helpful, we've seen what havoc is wreaked without it. And yet, when even the government has a tendency to treat the middle preferentially and rip off the little guy, it is clear that the discussion needs something other than a paternalistic debate about protecting the vulnerable. Nobody, not kind-hearted poverty tsars nor businessmen with a philanthropic bent, can really protect the poor from their impotence in a market. This question is political, not technical or regulatory, and ends in the question: how much poverty are you prepared to live with?