The news that the Swedish authorities covered up widespread sexual assaults by immigrant gangs on teenage girls at a Stockholm music festival, and possibly other incidents too, is immensely damaging for race relations in Sweden because it conforms so precisely to two stereotypes.

The first, widely believed in nationalist circles, is that immigrants to Sweden are responsible for the huge rise in reported rapes in recent years. The second, more true, and much more widely believed, is that you cannot trust respectable Swedish opinion to be honest about the bad effects of immigration.

It has been quite clearly established that there has been an increase in violent crime, and in reported rape, over the last 40 years in Sweden. In 1995, the first year for which statistics are easily available on the Crime Agency’s website, there were 179 murders in Sweden, of which 29 involved guns; in 2014 there were 317, of which 74 involved guns.

Some of the violence is closely linked to the appearance of gangs of Balkan and Middle Eastern origin among refugee groupings who fight for control of the drugs trade, among other things. There were around 40 unsolved gang murders on police files at the end of last year.

Swedish police accused of covering up sex attacks by refugees at music festival Read more

Rape statistics are harder to judge. The raw figures suggest a huge rise in reports, from 1,707 in 1995 to 6,697 in 2014. But, as the Julian Assange case showed, there is perhaps less stigma about reporting the crime than elsewhere, and the Swedish legal definition of rape is wider than in other countries. In any case, the police do not record the ethnicity of either criminals or victims, and the press is extremely constrained over reporting identifying details about either the victims or the perpetrators of crimes.

So it is impossible either to prove or to disprove, from official statistics, the nationalist claim that the rapists are disproportionately young male migrants. Yet that claim is repeated as a fact in racist and xenophobic parts of the internet. What is certain is that you would hardly ever find it mentioned, even to refute, in the reputable Swedish media – until last week.

This is the really damaging effect of the Stockholm scandal – and it is worth noting that only one of the reported assaults at the festival was classed as rape: most were mob gropings, which are still terrifying and criminal violations.

The Swedish political and media establishment decided to deal with the threat of a nationalist and xenophobic party, the Sweden Democrats, by ignoring them and hoping they would go away. This policy was fuelled partly by wishful thinking, partly by principle and partly by self-righteousness. It ended disastrously.

The Sweden Democrats broke into parliament in 2010 and now hold the balance of power there, although all of the other parties have combined to vote so as to neutralise them. The result of that, again predictably, has been that their support has risen to unprecedented levels – 20% in the last poll I saw. The recent clampdown on immigration can only strengthen them further.

The Social Democrats, and their newspaper, Aftonbladet, appear to have been particularly keen on the posture of suppression and denial, because the great majority of the Sweden Democrats’ voters had been Social Democrats, rather than traditional rightwingers.

It is absolutely clear – with the publication of internal memos by the newspaper Dagens Nyheter – that the Stockholm police failed to report the sex assaults at the festival for fear of worsening ethnic tensions. And it was understood by all parties that this would lead to an electoral advantage for the Sweden Democrats.

The organisers, who also allegedly knew what was going on, were concerned for the success of the festival and did not want to frighten away the teenagers who were its target audience.

So teenage girls were systematically assaulted and robbed by gangs of young foreign men because too many powerful people found their suffering was inconvenient. The result of this cover-up will be far more damaging than the truth could have been.