DJ Taylor: Arch calculator Dennis Tite is well known for his exactitude and considerable financial acumen

(Silje Eirin Aure)

10.45pm in the Dog and Firkin, Chislehurst, the last round's in sight and settlement is due. "Now, if you give me £1.65 and then pay for the drinks," Dennis instructs his firm friend Barry, "we'll be all square."

There are some amused looks around the beer-stained table, for Dennis – whose earnestness conceals not the faintest suspicion that anyone might find his calculations funny – is well known for this kind of exactitude. But Barry is a good-natured soul; aware that the two sausage rolls he consumed at Dennis's expense earlier in the evening were not intended as a gift, he pays up without complaint.

The taxi home is rather more complicated, as Rob and Martin are going on to Bromley, and Kev wants to be dropped off near Orpington high street, but the apportioning of payment is nothing that Dennis can't handle. Calculator at the ready, he swiftly decrees that if he and Barry pay £3.10 each, and Kev an extra 90p, then Rob and Martin are at liberty to take the taxi wherever they like – provided, this is, that Martin reimburses him for the football programme (£3) for which Dennis shelled out last Saturday afternoon.

It is not quite known where Dennis acquired his considerable financial acumen. His father, now dead, was free-handed to the point of carelessness and his mother, with whom, as a thirty-something bachelor, he now resides, is known for her liberal attitude to household expenditure. Yet little of this easy-going spirit has transmitted itself to their son, whose bedroom, beneath the posters of Bruce Springsteen and Jon Bon Jovi, is papered with Post-it notes reminding him of the coming week's obligations and the friends and work colleagues from whom some sort of tribute is due.

Hearing of the relatively well-paid job he holds down in the accounts department of a garden-centre chain, and the esteem in which he is held by his employers, casual acquaintances sometimes wonder why Dennis still lives at home. But for some reason the various romances on which he embarks rarely come to anything. It is not every girl who, after a week's holiday to Venice, for which it has been agreed in advance that the participants shall "go Dutch", can stand being presented with an itemised bill for €459 – even with the assurance that its compiler is ready to "forget about" the two bottles of water on the plane.