This mainstream strategy earlier proved a success in Belgium, the Netherlands and Austria.

Still, not less than 41 percent of Swedes voted for a different party in 2018 as compared to four years ago, and the 17 percent support for the Sweden Democrats may cause the end of the so-called "bloc politics", whereby a centre-right and centre-left bloc of political parties struggle for power.

It's even possible that new elections would need to be called within three months.

Swedish politics is very non-adversarial. For example, the budgets of the outgoing minority government composed of social democrats and greens were being supported by three centre-right opposition parties.

The centre-right Moderate Party does not want to continue to do so but then it isn't keen on joining a 'Grand Coalition' with the social democrats or seeing its 'blue bloc' splinter either. The SD's growing importance is upsetting a lot.

That this is all due to Sweden's open door immigration policies, which for a while saw 10,000 asylum-seekers per week entering the country of 10m inhabitants, is well-known.

A record 163,000 asylum seekers came to the country in 2015, the highest per capita of any European country. This followed hundreds of thousands in previous years.

Sweden, however, decided to shut its doors in November 2015, when green deputy prime minister Asa Romson cried at a press conference, as she announced the U-turn, commenting: "We simply cannot do any more."

Immigrants vote for anti-immigrant party?

Interestingly, even a lot of immigrants would be voting for the Sweden Democrats, which made efforts to attract them, a strategy which paid off, according to government agency Statistics Sweden.

In a way that's not surprising: immigrants are the ones living in the neighbourhoods plagued by increasingly violent gang crime.

The numbers of murders involving firearms have more than doubled since 2014, to 43, whereas Norway, a country half the size of Sweden, only saw one homicide.

This year alone, 10 murders happened in Rosengard, a district of the city of Malmo, where almost all crime suspects—and victims—are of foreign origin. It should perhaps be no surprise that the SD became the biggest party in the districts around Malmo.

The Swedish government denies that this is due to the recent immigration wave but voters don't seem to be convinced.

US president Donald Trump faced a backlash when he claimed in February 2017 that Sweden was struggling with crime and immigration, but ever since several Swedish researchers have been repeating the same line.

Prominent economist Tino Sanandaji explained that "until about three years ago it was a taboo to openly criticise migration and its consequences", but as "the burden on the social system dramatically increased" that has changed.

Claims that the economy has been doing well recently - so it's odd to see so much disgruntlement - do not tell the whole story.

When one looks at the economic growth figures per head, the results are much less impressive. Swedish annual GDP per capita growth in 2017 was the second lowest in the EU.

Sweden was the third-richest country on earth in the 1970s, but has since fallen back to 12th place, with poverty having doubled until 17 percent.

After decades of social democratic policies, with ultra-high taxes, a financial crisis at the beginning of the 1990s forced the country to embark on economic liberalisation, really going back to its pre-World War I laissez-faire roots.

A leftwing government even went on to scrap inheritance taxation and gift tax altogether in 2004.

The reforms have been a great success, but the work isn't finished, as Sweden's dysfunctional public planning of the housing market proves.

Add mass-immigration to the mix and it's not so hard to discover the sources of discontent, especially as 23 percent of non-European immigrants are unemployed, making them even harder to integrate and contrasting with a four percent unemployment of native Swedes.

An independent committee within the Swedish finance ministry has estimated that the net cost to public finances from most recently arrived refugees would be $8,000 (€6,800) per person annually over a lifetime.

The ongoing success of the Sweden Democrats is yet another reminder how chaotic migration has a great potential to upset society and political dynamics, possibly even more so than economic developments.

Whoever cares about the right to migrate and open borders should really keep this in mind.

Despite some misgivings now and then, Europeans support uncontrolled migration within Europe, maybe because the flows are all in all limited and because it is easier to integrate Europeans in Europe than non-Europeans.

Uncontrolled migration at a global level however, finds very little support. This is a reality which every European politician should heed.

Pieter Cleppe represents independent think tank Open Europe in Brussels