Not so very long ago, almost to the moment Northern Rock began to crumble, experts in the money business would explain the facts of life to anyone who cared to listen. Contrary to any of your misconceptions, they would say, there isn't much in the way of a serious return to be had from retail banking. Impressive, even mind-boggling, profit statements had given the man in the street the wrong idea entirely.

To hear it told, the willingness of banks even to bother with the nickel and dime stuff amounted to a kind of public service. Had they been truly rapacious they would have given up long ago on mortgages, overdrafts, kiddies' savings accounts and the posting of astonishingly expensive threatening letters. The real cash, one heard, was in the corporate game.

Strangely enough, however, a bunch of dodgy loans to some less affluent Americans - think of it as a kind of charitable giving - began to go a little awry. Suddenly, western capitalism (not to mention annual bonuses) had been put at risk. The world's finance ministers were facing the scariest moments of their careers. Throwing public money at banks became a patriotic duty. Mortgages and little people mattered after all. Just because of the less-affluent the global financial system, corporate bits and all, was seizing up like a rusty engine. And no-one was disparaging retail banking, or its fiddling small change. Perhaps, just possibly, an old, trusty, very convenient explanation had been overtaken by events.

Still, a good fairy tale is never to be scorned. The oil industry has its own version of banking's pat-on-the-head parable. In this one, giant petrol companies make no money - not real money, at any rate - from selling petrol to real people. "Better than expected" (better for whom?) quarterly profits for Royal Dutch Shell and BP come from production and distribution, you are told. The stuff that runs your car, heats your house, or keeps your one-man trucking business on the road is a kind of by-product. An epiphenomenon, if you prefer.

No call, then, for simplistic populism or a stray expletive when Shell admits to clearing $7.8bn (up from $6.9bn a year ago) in the space of 12 weeks. No excuse even for grumbling when BP ($6.58bn, a 48% increase) is making you proud to be British. Last year, while earning no money to speak of from you or me, Shell managed only a modest $27.56bn in annual profits, yet had to tolerate carping from the economically illiterate.

We'd be the ones trying to work out the difference between the various people who discover, extract, distribute and sell fuel when they appear - now you can call me naive - to be employed by the same firms, with all their sterling efforts appearing on the same balance sheets. Funny, that.

True, oil exploration is a fantastically chancy and expensive business. True, the government's cut in terms of duty amounts to a substantial chunk that has very little, if anything, to do with the environment. True, the margin enjoyed by big oil from a retail litre is a matter of mere pennies. As with the banks, however, these are not charities under discussion.

They operate, with some enthusiasm, in a society that regards comment on stupendous profits as bad taste. They thrive, in fact, in a world that rejects the deplorably simplistic habit of making connections between the obvious and the obvious. Like followers of some cargo cult, we are left to talk as though the oil price is a freak of nature, a bit like the weather, not a number stated on a particular invoice on a particular day with the expectation that hard cash will follow.

The dollar recovers and the price for a barrel subsides to somewhere (at the time of writing) between $118 and $119. Is this magic, an act of God, something entirely supernatural that has nothing to do with the profits returned by Shell and BP? When I take up turning water into wine - crude would be more rewarding - I'll try to believe it.

My sympathy for the haulage trade is, meanwhile, limited, most of the time. Nevertheless, if the basic cost of my business, the thing on which I depend utterly, had just shot up by 30% in less than a year, I might have been making my way to the Commons yesterday. I might even have concluded that if a New Labour government can be bullied once it can be bullied twice. Still, while an argument over fuel duty is worth having, a mention of big oil's profits would not go amiss somewhere in the debate.

Is the idea of a windfall tax now completely beyond the pale? Does anyone still believe that very big transnational firms would really quit Britain if an elected politician said Boo! to them? Put me down as a sceptic.

Put me down, meanwhile, as one who holds that, along with food costs, the issue of fuel is liable to do for Gordon Brown long before David Cameron gets his chance. The Grangemouth dispute, as I have said previously, was a reminder - and a warning. It counts, in fact, as elementary politics. First people are worried, then they are angry. And Prime Ministers should beware.

Everyone has a tale. That's the first thing you notice. People are muttering, exchanging notes, remembering, for once, that when middle-class professionals are disgruntled, there are others, many of them, who are a lot worse off. Neither group is offering three cheers to Royal Dutch Shell and BP this morning.

If the planet is relying on me for its salvation, things could get sticky. I try, though. The car is bigger than it needs to be, but we use it sparingly. Nevertheless, if a tank that needed £40 of filling last year now costs £60, will they please stop trying to tell me that the fact has nothing to do with an oil giant's profits? If my heating oil has gone up from 33.85p a litre to 45.95p, will someone explain how that kind of figure seems to the elderly or the less-rewarded?

I can still guess at the answer. I can also grasp that companies capable of making billions often have to spend billions. But, as with the banks, there is a certain strange pattern to the distribution of burdens, of effort and reward, where our national champions in oil and a pensioner wondering over 45.95p a litre are concerned.

Aggrieved truckers in Park Lane, rarely mistaken for sunbeams, are the first signs of a storm for Mr Brown's administration. Most of the things said about energy security overlook the personal, the mundane and the daily grind of feeding a family or heating a house. The oil giants may be taking a "better than expected" profit, but you could be forgiven for believing that they are taking something else, too.

Those lovely quarterly numbers are unearned, more or less. They count as evidence of a windfall in anyone's terms. It is not enough to talk about the mystical process of supply and demand when very large industrial concerns can, and do, dictate both. It is certainly not good enough to talk theory when real people have real fears.