Manners have not yet been made redundant by mobiles

As with any innovation, it takes time for conventions and rules to catch up with the technology. It's now illegal to use a phone (without a hands-free kit) while driving, for example, but not when cycling. I don't recommend it, though; I almost ran over a cyclist the other day who suddenly swerved into my path. As I passed him I realised that he was texting as he veered from side to side across the street.

Most of the questions presented by mobile phone use are not, as that sort of thing has the potential to be, matters of life and death. There are also some instances – such as communicating by Twitter or Facebook with someone who is actually in the same room – which, though fairly harmless, are patently absurd. (That's not a theoretical example, though: ask a teenager.)

More interesting is the recent case of Jo Clarke, a 26-year-old property manager from Crayford in south London, whose experience in the checkout queue at her local Sainsbury's seems to have divided the nation fairly evenly. Ms Clarke was talking on her phone while waiting to put her shopping into bags, when the woman behind the till said that she would not check her items until she got off the phone.

According to Ms Clarke, she said: "Apologies, I didn't realise that it was Sainsbury's policy that you are unable to use your phone at the checkout," to which the checkout operator replied: "Well, you learn something new every day." Ms Clarke then checked and discovered that there is no such policy. The employee concerned was given a reprimand, and Ms Clarke was offered an apology and some vouchers – though she is in the huff about her treatment, and is going to go to Waitrose in Dartford from now on.

My immediate impulse was to side with the supermarket employee, since it seems appallingly rude to talk into, or tap away at, a mobile phone when you are engaged with someone else. But then, as Stephen Fry once pointed out, the telephone is an intrinsically rude invention; its ringing is the exact equivalent of somebody constantly shouting "Listen to me!" until you give in to them. It's bad enough installing such a thing in your home; carrying one about with you is tantamount to an open invitation for anyone to pester you at any time. This often seems to be someone with a strong Indian accent called Kevin who wants to talk to me about a fault he has detected in my Windows operating system, which is odd, since I haven't got a Windows operating system.

So I was surprised that 50% of people (in my completely unscientific tally of chatter about the case) took the opposite view, and thought that the checkout operator had been at fault. Having thought about it for a moment, I concede that inventing a non-existent policy to put someone else in her place is not really the acme of customer service, while the comment "you learn something new every day" has the authentic, triumphalist tone of jobsworths everywhere. And while commercial operations can and do impose restrictions on their customers, customers are free to take umbrage at such attempts to control their behaviour, and to take their business elsewhere.

Now I find myself torn. Perhaps, as Henry Kissinger said of the Iran-Iraq war, "it's a pity they can't both lose". But I think the chief reason why there are plausible arguments for both parties in this case, and that I find my sympathies wavering, is that the encounter can be viewed in two different ways, each of which puts a different party in the position of power.

Viewed as a commercial transaction (which is of course what it is), the power is being held by the checkout operator, who abuses this position in order to dictate the customer's behaviour. And that seems wrong because the power in that relationship ought to belong to the customer rather than the employee – as Ms Clarke's decision to go to Waitrose instead demonstrates. In this particular case, the wrongness is amplified because the store did not in fact have a policy, so the employee was simply attempting to get her own way – whether for her own convenience, or because she was having a bad day, or out of bloody-mindedness, or because she didn't like the look of Ms Clarke's face.

But viewed as a social encounter between two human beings (which of course it also is), the scenario is reversed. On this view, the person in control of the situation is the customer. And though that is as it should be, our sympathies – or at any rate, my sympathies – then lie with the supermarket worker. That, I think, is because the fact that it is a contractual encounter is secondary to the importance of basic human interaction, and on that basis, the customer is failing because she is being rude to the worker. Indeed, it is the very fact that the customer should always be regarded as being in the right, or at least the more powerful party in a commercial exchange, is precisely what imposes a social duty on her to be civil.

The social aspect of the exchange may not trump its primary character, which is business, but that is the reason why manners exist. Unfortunately, most encounters in the modern world between customers and shopkeepers and others who are being employed to provide them with a service are not genuine social exchanges. But that is not licence for the customer to be rude; good manners may be a pretence, but they are a necessary pretence, disguising the essential nature of the encounter.

It is precisely because it would be insupportable to emphasise the true nature of such exchanges that most of us, for example, think that people who are rude to waiters are odious. Not to be polite, and to engage in the pretence that an unequal meeting for a commercial transaction is in fact a social meeting of equals, is wrong because it subordinates our shared humanity to the nature of the transaction.

Manners are the mechanism by which we acknowledge each other's value. A smile, a please and a thank you have not been rendered redundant by the mobile phone.