Somewhere from above there came a voice: "Pivo?" ("Beer?"). It was the waiter, and I suddenly realised why in the Czech Republic and in Slovakia they call waiters "Pan Vrchny" ("Mister Upper"). U Fleku's Mr Upper, sporting a short-sleeved white shirt under a black vest, was towering above me, holding an enormous tray with several dozen beer mugs on it.
His question was rather a rhetorical one; why on earth would someone come to U Fleku, if he didn't want beer? To play snooker? To board a flight to Bratislava? Or to scribble away in a WH Smith recycled notebook, as I did?
Thump! A weighty mug with dark brown liquid landed on the table in front of me. It was followed by Mr Upper's dextrous hand which made one quick notch on a piece of paper, stuck under my coaster.
Before I could say "Dekuji!" ("Thanks"), another Mr Upper's hand was stretching towards me with a shot of Becherovka liqueur. But I was well prepared for the trick. Gently pushing his hand away, I told him resolutely "Ne!" ("No!"), as the Pub Etiquette section of the Prague Post newspaper advised.
"Perche?" Mr Upper asked in unexpected Italian. "Because I don't want it!" I replied in English. "But it is very good with beer," the obstinate polyglot insisted.
"I don't think so. Take it away!"
The reason for Mr Upper's persistence was that they charged you 200 crowns (pounds 5) for a shot, the price of a three-course meal (with beer) in a good Prague restaurant, whereas a 0.4 litre mug of beer at U Fleku was "only" 39 crowns - by far the most expensive in the Czech Republic, even though just less than a pound.
Besides, contrary to Mr Upper's assurances, mixing the vomitingly sweet Becherovka with beer was like eating a pickled herring topped with raspberry jam. Ten years ago they didn't do this to unsuspecting tourists. Capitalism can sometimes be pushy.
I took a couple of sips from my mug and found the beer surprisingly pleasant. Its bittersweet taste reminded me of kvass, a drink of my Ukrainian childhood. This is a mildly alcoholic drink made of yeast and black bread. I stopped drinking it when one day I saw a kvass tank break in two and all its contents pour out: the streams of brown kvass were swarming with white intestinal worms.
Meanwhile, my neighbours were busily gulping their Becherovkas, washing them down with beer. Several happy Mr Uppers were hovering above them like butterflies, and the rows of pencilled "notches" on their beer slips were as thick as hedges in Devon. The sugar daddy was quarrelling with his bovine-necked Brunnhilde, whose face was by now pretty bovine, too.
The famous U Fleku, which claims to be the oldest beer pub in the world, was clearly no longer a place where one could find much local colour.
Not far from U Fleku, in Kaprova Street, I spotted a small pub called U Mestkiy Knihovni ("At a Local Bookshop"). What an ingenious name. Imagine an angry wife questioning her wayward husband: "Where have you been all evening?" "At a local bookshop," he answers meekly. I didn't venture in, but through the window I could discern several fat, red-faced men drinking beer. And not a single book.
My next destination was U Pravdu, which translated as "The Truth". My guidebook promised a nice beer garden and a convivial Svejk atmosphere. The beer garden was closed, the pub was totally empty, and this was the whole truth about The Truth.
I was luckier at U Cerneho Vola ("At a Black Ox"). The atmosphere inside the pub was warm and brotherly: under low, beamed ceilings, the patrons were sitting on long dark-wood benches. They were drinking Kozel (Goat) beer and chasing it with traditional "Pivni syr", a strong, spicy goat cheese.
The balance, as I soon discovered, was perfect: my mouth was set on fire after each bite of the heavily peppered cheese, and the only way to put the flames out was to wash them down with a good gulp of Kozel. The man next to me had six notches on his slip already, and was thirstily approaching his seventh. A large mug of beer cost 8.40 crowns (20p) - a big difference from U Fleku.
Through a small leaded window, I could see the palatial Foreign Ministry building across the road. It was there, in the courtyard, that the body of the country's democratically elected president, Jan Masaryk, was found beneath an open window on 10 March 1948. It was officially announced that he had killed himself by jumping to his death.
The death of Masaryk was the final episode in the communist takeover of Czechoslovakia. Rather than a suicide, it was the last (so far) case of a centuries-old Czech political tradition of defenestration, which means chucking an undesirable politician out of a window and making it look as if he has taken his own life. The first defenestration, a collective one, was in 1419, when several over-zealous Prague town councillors were hurled out of a window by a group of bullish religious reformers. Since then there have been three more.
It is hard to say who is going to be the victim of the next great defenestration of Prague, although when I was there many Czechs believed it was likely to be Vaclav Havel, beer-loving former dissident, playwright and incumbent President of the Republic. Some time ago, he even won the honorary (if somewhat dubious) title of The-Most-Likely-to-be-Defenestrated Person in Prague.
After a mug of strong, pale Korzel, I started clearly seeing human bodies - in suits and ties - flying out, one by one, from the Foreign Ministry's windows. I needed a cup of coffee. "What will happen if I order a coffee here?" I asked my beer-swilling neighbour, who happened to speak some English. "They will think that you are an alcoholic," he replied, finishing off his tenth mug.
This is an edited extract from `Borders Up!', Vitali Vitaliev's bibulous travelogue through Eastern Europe. It is published next Tuesday by Scribner (pounds 9.99). To get to Prague: Czech Airlines (0171-255 1898) flies from Heathrow, Stansted and Manchester, with fares starting at pounds 185 return from Stansted for travel in May. British Airways (0345 222111) and British Midland (0345 554554) fly from Heathrow. Buses from the airport to the city leave every half-hour. Get off at the first stop, Dejvicka, to link into Prague's Metro system, or stay on to Revolution Square for destinations to the east of the city centre. You can travel by bus from London - a journey of around 18 hours - on Kingscourt Express (0181-673 7500) for pounds 85 return