I was in Stockholm a week last Friday - an eyewitness on the great night that nothing happened. Donald Trump gave a speech in Florida the next day, asking his audience to look at what had occurred "last night in Sweden".

Something appalling, apparently, involving asylum seekers. The Swedes "took in large numbers," he said. And now "they're having problems like they never thought possible". But he was wrong: nothing of note had happened that night. His mistake was used by much of the Swedish media (and politicians) to slate him, as if he concocted the whole idea of an immigration problem.

The mockery lasted for days: what event could he have been referring to?

Were some meatballs burned in Uppsala? Did an Ikea run out of Billy bookshelves? "What has he been smoking?" asked Carl Bildt, a former prime minister. He could almost have asked: Crisis? What crisis?

The inside pages of most Swedish newspapers would carry the answer. Early last week, for example, a riot broke out in one of Stockholm's suburbs, ending in a photographer being injured and a policeman opening fire. There were also stories about how six Afghan child refugees had committed suicide in Sweden in the last six months, failed by a government system that cannot cope with the 25,000 unaccompanied migrant children in its care. All this is shocking - but in Sweden nowadays, not so surprising.

Sweden is not a country that is falling apart. You can still land in Stockholm's gorgeous Arlanda Airport, skate on the frozen lakes in special lanes polished by the local authorities, cook sausages on the communal barbecues. The Scandinavian paradise is still there, welcoming and inspiring. The government has, after great upheaval, managed to cut the refugee influx by four-fifths. But its failure to integrate those already there has led to another Sweden, a country within a country characterised by gang violence and joblessness.

It's easier to ignore this in Stockholm than it is in Malmo, a smaller city which has long been the first port of call for immigrants who arrive over the bridge from Denmark.

On the day I arrived in Sweden, a 23-year-old was murdered in the city square there, shot in the head in front of several witnesses. It was the third such murder in six weeks. The local press tends not to report the ethnicity of the victim or suspects in such attacks, but Swedes have learnt to recognise immigrant-related gang crime when they see it.

Foreigners who visit the wrong part of Sweden can pay a heavy price: last summer a British boy was killed in a grenade attack in Gothenburg as he slept with his family.

If grenades were being thrown into children's bedrooms in Athlone or asylum centres were being torched in Meath, the immigration debate here might be a little different. The word "crisis" might be used. But what's striking about Sweden is how defensive policymakers are when confronted about all this; how insistent they are that things are under control. As the violence affects just a sliver of society, the overall Swedish crime figures are quite small. Trouble can be buried in the data.

Wider discussion about all of this is also discouraged by what's known as Sweden's 'opinion corridor' - the narrow parameters into which public debate is confined. Those who step outside, and talk about the immigration problems, risk being accused of bigotry. Or, perhaps worse, giving succour to the more populist Sweden Democrats, the party now supported by one in six Swedes.

The immigrants do want to work, but find themselves stuck outside a heavily regulated jobs market that could have been designed by a populist demagogue to keep them out. For unskilled work in restaurants, for example, the trade unions' unofficial (but strictly enforced) minimum wage is about €11 an hour. For unskilled immigrants, especially from countries like Afghanistan and Somalia with no properly functioning education system, this means the Swedish dream ends before it begins. A policy intended to lift everyone's wages has ended up destroying entry-level jobs, and ensuring thousands of immigrants are shut out of the economy, denied the first rung on the ladder to work.

Among Swedes, unemployment is about 4pc and falling. Among immigrants, it's 22pc. No developed country has a higher differential.

The Swedish government describes itself as a "humanitarian superpower" and accepted refugees on that basis, but its fatal mistake was to welcome so many without being able to integrate them. Hence the zones of joblessness and the criminality, and the inability to know what to do about it.

The resulting shadow society is now quite advanced, with its own moral codes and even its own legal system. Tribal courts are now in operation, dealing with crimes - or, at least, what count as crimes in the underworld. The fine for attempted murder is about €59,000, according to Malmo's chief prosecutor. Of the 37 murders and attempted murders in the first half of last year, just seven have been solved. But what are police to do, when witnesses drop out and victims drop the charges? Officers admit that, when child refugees go missing from care homes - feared to have been passed into prostitution or criminal gangs - there is not much they can do.

In so many fields - technology, music, retail - there are Swedish firms leading the world. But its social model, created from the best of intentions, has ended up incubating a violent underworld into which immigrants are being ensnared. As a friend of mine puts it, Sweden is still "10 parts heaven to one part hell" and you can avoid the hell (if you're not a refugee). But the problems it now faces are those of shadow societies, mafia courts, gangland killings and conundrums like how to handle adult refugees who turn up with a child bride in tow. And how to pacify suburbs that are slipping out of police control.

These issues all fit a certain description. They all stem from Sweden's decision to take larger numbers than it could cope with, leading to problems that were once never thought possible. It will pain the Swedish government to admit it, but on this point, at least, Donald Trump was right.

Telegraph.co.uk