"We are being labelled traitors," says Jannek quietly, sipping a coffee. "We have been threatened, they say they know where we live and our cars will be burned."

Jannek – not his real name – claims he is being targeted because he is one of the few people to criticise the growing wave of foreigner bashing in Berlin.

Affluent expats and tourists from Italy, Spain and the UK are being blamed for the city's turbocharged gentrification. This has mutated into physical attacks and abusive graffiti ("yuppie scum" being a favourite) in trendy but poor frontline areas like Kreuzberg and Neukölln.

It all started about two years ago when anti-tourist graffiti appeared in bars, cafes and on the street. Around the same time, says Jannek, bars started posting "no hipsters or tourists" signs on their entrances. "Then people started saying 'we can't stand any more of these people', meaning tourists, hipsters or 'long-time tourists', making no distinction between them," he adds. Then the attacks on hostels and hotels began, accompanied by verbal insults against individuals in the street. Latte-serving cafes have been attacked with bricks and bottles, he says.

Last year an estimated 6,000 people marched peacefully through Neukölln to protest against soaring rents.

Many of the aggressors are not from Berlin, they just got here first, says Jannek. He tells me of a Berliner who attacked a "tourist" on the underground – and they both turned out to be from the city.

A few months ago Jannek, who is neither a hipster nor a foreigner, set up the underground political group Hipster Antifa Neukölln with four others, an anti-fascist movement tackling the growing hatred. He believes that much of the anger is spearheaded by other anti-fascists. The punks of Kreuzberg, who once built their ideologies around a hatred of Nazis and right-wing thinking, are using this same energy to blame tourists for driving them out of the neighbourhoods they love.

"The anti-foreigner thing started as a bit of a joke but now it is much more serious," explains Jannek. "This is critical, it is sneaking into mainstream thinking – it's almost being perceived as normal to dislike tourists.'

So far the group has organised two lectures this month – the first is today, the next on 11 December – with leading thinkers on city dwelling and gentrification, such as Roger Behrens, who wrote Gentrification und urbane Bewegung, to highlight the issue. The group has also documented the attacks and abuse. Their stickers read "Everyone is welcome – party like it's 1945" and can be seen in toilets across the city. But this is also a city where you can buy a "Welcome to Berlin – Now Go Home" lighter for €1.49.

Known for its relaxed atmosphere, cheap prices and hedonistic party scene, the German capital is a magnet for international creatives and layabouts.

The figures speak for themselves – numbers of international visitors to Berlin jumped by 13% in the first half of 2012 from the same period last year. Residential property prices in the city have jumped a recession-busting 32% since 2007.

Kreuzberg, once one of the city’s poorest areas is now the epitome of cool, with self-consciously ramshackle bars like the Barbie Deinhoff

The fall of the Berlin Wall created a bipolar city, a mixture of rich and poor. Once wedged against the west side of the wall, Kreuzberg was one of the city's poorest and most densely populated areas in the 1970s and was largely forgotten in the early 90s as people scrambled to the former East Berlin areas like Mitte. Now Kreuzberg is the epitome of cool, a self-consciously semi-derelict hub of arts, ramshackle bars like the neon pink Barbie Deinhoff and clubs, including the world famous (and notoriously difficult to get in to) Watergate, nestled by Oberbaumbrücke bridge.

With the cheap rent drying up in Kreuzberg, many young people are looking to neighbouring Neukölln, once an affordable, bustling haven for immigrants from Turkey and Russia. Now the legions of kebab shops are becoming peppered with tastefully rundown bars full of international chatter, with the lengthy Weserstrasse running from Hermannplatz U-Bahn rapidly transforming from sleepy backstreet to a party hotspot.

"It's OK to be angry about gentrification but we want to get people talking about possible solutions, not throwing rocks," says Jannek. "We don't support gentrification, we want to stop it, but it is not a new phenomenon. Policies are to blame, not foreigners. Investors, bankers and politicians are partly to blame. We need to be progressive and make laws to cap rents to help the poor.'

In the short time that Hipster Antifa Neukölln has been active it has attracted huge media attention in mainland Europe, including German daily Der Tagesspiegel, Dutch magazine Vrij Nederland and Berlin's Radio Spaetkauf – a small victory says Jannek. "We have seen some changes, some people distancing themselves from anti-tourist thinking. Ultimately who is a Berlin citizen? Everyone is if they want to be here – you have a right to be where you want to be."