Tourists seeking a peaceful and historical city break have long been drawn to the beautiful cobbled streets of Bruges. But recent arrivals to the beautiful Belgian city may have had the tranquility shattered by incongruously ugly clashes between rival groups of tour guides battling for their cash.

The city’s certified guides, who can spend up to three years earning the right to wear their official badges, have become enraged by untrained men and women turning up with umbrellas offering free tours, with a cup on hand to encourage tipping.

In response, the traditional guides, who work for the Gidsenbond, or guide association, are alleged to have deployed an array of dirty tricks to defend their territory.

Tour groups led by the free guides are being infiltrated by wily old hands who pose difficult questions, in the hope of shaming their rivals out of town. It is claimed that the newcomers have been chased around the city, or their customers made to listen to endless heckling.

A deleted Facebook entry from one of the traditional guides reportedly asked: “Who wants to set up actions against the pirates? Follow them with a loudspeaker, repeat everything, say they cannot walk on the grass in the Beguinage [houses inhabited by nuns and other unmarried women]. A little Pokemon-hunting in Bruges, but in real life. Who wants to take part?”

Frank Poelvoorde, a spokesman for the free guides, claimed the situation had got out of control. “It has got worse and worse. They infiltrate our groups, and intimidate us and the tourists. But this week they have gone too far.

“A Spanish guide, a young woman, was physically attacked by an official guide … She was pushed several times, even on the face … Female guides no longer dare to enter the street [in case they are] physically attacked. Can you imagine that? In Bruges?”

Jo Berten, chairman of the Gidsenbond, told the Belgian newspaper Het Nieuwsblad he did not know who was involved in the alleged incident. “But if it happened, then that is not right,” he said.

“Bothering colleagues: I resist that. On the other hand I understand the frustration. Our guides must attend three years of evening school and do final work. And then suddenly someone next to you who has read two A4 pages and does the same work? Why would you still do that course?”

There are believed to be 2,000 tour guides operating in Bruges, where a registration system has been recently established.

The city’s mayor, Renaat Landuyt, said: “I know that there is tension between the guides. But I also continue on what the police tell me: no significant incidents have yet been identified. Except for angrily looking at each other.”