"Cauliflowers are too expensive for the likes of you," he would say, proffering a cabbage instead.
I never really understood the logic of it. Did he keep the cauliflower lest a visiting plutocrat should venture up the little road in Highbury where his shop stood? Was the margin on cabbages better?
Had we looked wealthier, would we have been forbidden the cabbage as being too cheap? Were the words a signal set by MI5 and did he expect us to reply: "But at night all cats are grey."?
I don't know how it worked and neither, apparently, did he, as his little shop soon disappeared. Perhaps he is now chief executive of GoBank.
What is clear is that the system could be developed to operate more widely.
Before the app can operate, you have to key in your budget. Perhaps you could give other details, too, accompanied by a photograph.
"Going to lose some weight then," the phone would exclaim as you reach for the size that fitted so well a year or so ago.
Or "Cream on pink skin, going to a fancy dress as a peach melba are we?"
Perhaps you could give it your grades as well - "Brief History of Time? Wouldn't you be better off with a Jeffrey Archer?"
Or religious inclinations - "Someone like you going on holiday in the Middle East. I am afraid I am automatically programmed to notify the CIA, so stand in the car park with your hands up."
Well, no doubt it will be a long time before it gets that far.
Meanwhile, it will certainly increase mobile phone sales. Those who have used the app, thrown their phones on the ground and stamped on them, will be in need of replacements.
Before retiring, John Watson was a partner in an international law firm. He now writes from Islington, London.