Every hack wonders sometimes if it's all worth it. Every now and again, you get an assignment so tough you have to spend the next day in bed to recover. In-depth research can leave you with all the sweating, queasy, headachey signs of major illness.

I conducted some in-depth research on Wednesday with Ian Wisniewski, the vodka man. Ian and Nicholas Faith have just completed an exhaustive survey of the spirit under the title Classic Vodka (Prion Books, pounds 9.99). Aha! I thought. That'll make a feature. Quick interview, run-down on the qualities that differentiate the tipple of kings from the stuff swigged in bus stations. Ian had a better idea. "I'll meet you in the Tsar's Bar," he said. "Then you can have a practical demonstration."

It started beautifully. Six o'clock at the Langham Hilton, white suit with shocking pink accessories. Ian, cool, blonde and immaculate, sat majestically at a table. A nice man pushing a trolley disguised as a dressing table - scent bottles and powder-puff jars full of olives - made a "Tsartini" with a jalapeno in it. It did wonders for the chest hairs. I found my notebook. "So tell me about vodka. Was it difficult researching the book?"

"Oh, no," he replied. A pair of glasses appeared, one filled with stuff called "Seriously", the other brimming with Blavod, which is black. "It's fascinating. Every vodka has a story attached to it." He spent much of last year in the Warsaw distilleries. "It was great fun. Although sometimes it got a bit strange when you found yourself swigging 96-degree proof vodkas just after breakfast. They don't provide spittoons, you know. It would be rude to use one."

An iced bowl of shots of Sibirskaya, Gorilka, Wyborowa and the bar's own Fruits of the Forest landed in front of us. "Gorilka is the Ukrainian for burning," he said. "They have loads of different flavours from the raw ingredients. Polish is mainly rye, Russian and Scandinavian mostly wheat. The Poles grow a special type of high-starch potato specifically for vodka-making." We sampled some Bison Grass ("You can't cultivate it. The yields are lower than if you harvest it from the wild") and Goldwasser, which contains flakes of 23-carat gold in deference to the medieval belief in the metal's medicinal properties.

Everything was going swimmingly. "This is lovely," I said. "I haven't had this much fun doing a piece in years." "Perhaps," he said, "We should have Martinis." "You're the expert," I replied. We poured into a cab, which took us to the Metropolitan.

The Met is jolly, red and full of bucket chairs. The bucket chairs are full of bums you have sneaking feelings you should recognise. The exhausted blonde next to us turned out to be Mariella Frostrup. We perched on stools. Mine seemed to have a wobble. Ian tried it. It didn't wobble for him. An army of crop-haired young men in - get this - black Donna Karan uniforms moved and shook, dashing vermouth from vinegar shakers into glasses and throwing it out again. They have three sizes of glass - mini, medium and greedy - and 24 Martinis on their list. We started with a Polish, moved on to a Sake, which had a twist of cucumber peel floating in the bottom. I fished it out with my finger and chewed it.

A raspberry and a melon Martini later, I was assuring him that vodka was the only drink I'd ever touch. "It's all delicious. Everything. All wonderful." He nodded sagely. A mixologist strolled past with a mechanical spoon on a stick. "Darling, let me play," I begged. Whirled it around a couple of times, then tried it on my companion's ear. "Euugh, tickles," he said, and ordered a round of Dirty Martinis.

My elbow slipped off the bar. I would have felt like Audrey Hepburn in Breakfast at Tiffany's, except that Audrey's white trousers would never have had developed mysterious grey flecks. Ian seemed neither shaken nor stirred. "Let's go to The Foundation. You have to try some cocktails, and they have a fountain."

In the basement of Harvey Nick's, where the bottle shelves are indeed backed by a mirrored wall of flowing water, I had a Purple Haze and a Foundation Vodka Punch, and my notes say something like "vod gin blue curac dsh pnk snaps lem lim eggwht lmade grenad", so obviously the old professional dignity remained intact. Then, suddenly, the bar was closed. "Aargh, they close early," I moaned. "Uum," said Ian, "It's twenty-five to twelve".

Fumbling on my front doorstep, I tripped over a food parcel from Asda. Inside was a bottle of the coolest thing ever: County Cream strawberry cream liqueur, a sort of added-value Bailey's. Coat on the floor, keys in the goldfish bowl, I poured a tumbler: melted Haagen Dazs with booze. So delicious I had to ring Angelboy to tell him. A sleepy voice answered the phone on the eighth ring. "Darling, did you know that you can only grow Bison Grass in the wild?"

A pause. "You're completely smashed," he said. "Go to bed."