'The punters are surging up and down the aisles like spring tides'

The setting: a huge Christmas fair near Malmesbury. The challenge: to sell copies of your own book. The technique: think of yourself salmon- fishing...

Without raising my head I can see a woman steering straight for our table. A day and a half at this game have taught me that timing is vital.

It's exactly the same as salmon-fishing: when you feel a fish take your fly, every instinct tells you to strike - but in fact what you must do is wait. So, now, I tell myself, do not look up too soon. Here she is, in front of our left-hand show-card. I raise my head and give a glowing smile.

Waste of time and effort. The woman - a large, middle-aged person wearing a dark-green cardigan and skirt - is glaring sideways at the card with an air of incomprehension. I see her lips mouthing the title of my book - When the Country Went to Town.

"What's it about?" she barks, in a sharp baritone.

"Well - the countryside marches, and the rally in Hyde Park on 10 July."

"Is it any good?"

What the hell is the answer to that? After rapid sifting of various alternatives - "Brilliant", "Rubbish" - I come up with the feeble "Not a lot!"

She grabs a copy and glares again. Just as I am gloomily deciding she has no interest in country affairs, she suddenly says, "All right - I'll have five."

Five copies at once! Ye gods - a bonanza. A peep into the customer's bag reveals that it is stuffed with pounds 20 notes. My publisher, David, takes her money while I scribble five signatures on the title pages - and then we both eagerly scan the crowd for more of her ilk.

The scene is one of the Christmas fairs run by that redoubtable organiser, Mary Howard. To have yellow AA signs made out simply with your name on them, you must be a big cheese - and she is: by her own efforts she has raised some pounds 350,000 for charity, and her fairs make pounds 50,000 a year for charitable causes. So the road signs say simply "Mary Howard", funnelling fans into Hullavington airfield, near Malmesbury.

The fair is in one of the hangars: an amazing structure about 300ft long, nothing but a gracefully curved roof, which sweeps right down to ground level on either hand. Inside, the press of punters is terrific: wild- eyed, and 98 per cent female, they surge up and down the aisles like spring tides. When word comes round that today alone nearly 3,000 have paid the pounds 4 entrance fee, I can well believe it.

But how does one engage their attention? Jump up and down? Gesticulate? Shout? Smirk? Look the other way? Grin like an ape? Stand up? Sit down?

Professional shop-keepers doubtless have their methods, but for a beginner, the uncertainty is hell. David has a theory that it is essential to keep our table well stacked with piles of copies - a state of play which (a cynic might remark) is all too easy to maintain.

My mind wanders to the disused airfield outside. I keep thinking how, over in East Anglia, the Thurlow Hunt has just won a major conservation award for its rehabilitation of a Second World War bomber base: there, volunteer workers have broken up the old runways and returned the land to grass, corn and trees. Will that ever happen here at Hullavington? Or will the vast, level expanse be used for houses, in preference to more scenic areas, as many people feel it should?

Look out, though. Concentrate. Here comes an obvious countryman: red face, hefty build. He takes one look at the book and says, "I should think that's pretty boring."

For a moment I am speechless. Then I come back with, "It's fairly light, anyway".

Bright blue eyes fasten on me.

"In fact," I blunder on, "it's so light you more or less have to hold it down to read it."

No spark of amusement softens that stare. Off he goes, clearly with the impression that I am crazy.

Feeling in need of a stiff whisky, I mutter to David, "No more jokes", and square up to a girl of about 16. Even if she is penniless, at least she has a lively face.

"Were you at the rally?"

"Of course!"

"And on one of the marches?"

"The day from Stow-on-the-Wold."

"Great!"

Immediately she buys a copy for her boy-friend. "He wasn't in Hyde Park," she says, "so please write something really rude in it."

"What - like 'Up yours'?"

"Not as rude as that."

She settles for "Mark - Where were you?". Then suddenly she says, "Oh, look. I need two more". She pays cash, professes herself delighted, and is gone. With time to study the throng, we notice the same people coming past again and again. They are in slow orbit, searching for Christmas presents with ever-increasing desperation. Several raise my hopes by veering in towards us, but then cry out: "Where's the canteen?"

By 5.30pm, after seven hours on duty, I have had enough. I decide I am not cut out for selling.

Napoleon famously dismissed England as "une nation de boutiquiers". But did he realise what physical stamina shopkeepers need, to stand around all day; what mental reserves they must have, to combat lack of trade, boredom and insults? I salute them - even if, at the same time, I am profoundly glad that my stint behind the counter is over.