The sign taped to the window at Legends Bar reads: 'Please, no groups of drunken British men allowed'. On the street outside, six men are loudly and lewdly casting aspersions on the sexuality of the Czech bar owner before they stumble off in search of more welcoming premises.

Theirs is not the only stag party drunkenly wandering the cobbled streets of Prague this weekend. In fact, the city has become so popular with badly behaved Englishmen looking for a cheap bash that Czech officials have unofficially approached the British authorities to complain.

With airfares to the Czech capital plummeting, the number of flights from the UK has spiralled, and the number of violent, beer-soaked Brits on debauched weekends away are becoming a serious concern.

The Czech Ministry of Foreign Affairs is urging Whitehall to do something about the rising level of crime committed by British men. Several hundred descend on downtown Prague each weekend, attracted by cheap flights, cheap beer and cheap sex. With prices about a fifth of those in the UK, the city has become a hotspot for stag nights and sports team parties.

'We are communicating the problem with British authorities to try to find ways to stop British men behaving violently in Prague,' said a senior official of the Foreign Ministry.

And the problem is about to get worse. With air tickets available from only £11.50 by budget airlines, numbers are growing. Reacting to the demand, EasyJet is increasing its flights to Prague to five a day by the end of March.

By Czech police estimates, a quarter of flights into Prague over the weekend will have included party-bound groups of British men.

'They don't fight among themselves as much as they fight with bar staff, mostly because they think the bill is too high. They get angry and destroy something,' said Jiri Sellner, Prague city centre's police chief. 'Italians are wild, Dutch are wild, but Britons are the worst.'

It is not hard to see why. 'Prague Piss Up', run by two Britons, organises stag nights, brewery tours and shooting lessons in Prague. Among its offerings is a strip show and meal.

Or, you can get a guided tour of Prague pubs for £20, including 10 free beers. 'You will spend about five hours travelling around the old town, taking in the sights and getting pissed.'

But several bar and restaurant owners in the city centre have rolled up their sleeves and are taking action. Most have strengthened security and the signs on the doors prohibiting British men are becoming more and more common.