During the last election David Cameron made great headway with his slogan about Labour and the SNP wanting to “break up Britain”. It’s been a theme with him. As leader of the opposition, Cameron declared Britain “broken” under Labour, and said he was the one to fix it. It’s ironic, then, that few people in the past decade have done more to break apart the bonds that hold Britain together than the Tory party leader.

Responding at Wednesday’s Prime Minister’s Questions to Jeremy Corbyn’s visit to the refugee camp at Calais last weekend, Cameron joked: “They met with a bunch of migrants in Calais. They said they could all come to Britain.” Corbyn had travelled to Calais to witness for himself the appalling conditions endured by those at the camp, by people who have already fled war or extreme poverty, and survived treacherous journeys across Europe and the Mediterranean. Britain and France need to be “a bit more human about this”, Corbyn said.

But Cameron was not interested in their humanity – lumping them, their stories and their suffering into a “bunch”, mere fodder for his jokes. On the day he commemorated Holocaust Memorial Day one couldn’t help but wonder whether, if Cameron had been around in the 1930s, he would have laughed about “a bunch of Jews”.

It was remarkable, even though we already knew Cameron’s views on migration: last year he called those trying to gain entry to Britain a “swarm of people” – another attempt to dehumanise. And in response to the refugee crisis across Europe, and the public horror over the death of two-year-old Alan Kurdi, he approved only a miserly 4,000 entries per year.

Muslims seem a particular target of his divisive and alienating language

Muslims seem a particular target of his divisive and alienating language. Today’s comments come a week after Cameron’s ill-judged threats to deport female Muslim migrants if they don’t master the English language, and on the day his chief schools inspector warned that schools may be failed if they allow girls to wear face veils. “This will have the effect of alienating many staff and pupils,” said an NUT spokesman. Andrew Clapham, an expert on school inspection, said: “There is no credible evidence base to suggest that wearing a piece of clothing on one’s head has an impact on intellectual or academic ability.” But already the damage has been done: an issue that affects a tiny fraction of Muslim girls, has become headline news. Indeed, BBC Radio 5 Live chose it as their main phone-in debate today, creating the impression that it’s a large-scale problem.

At a meeting of the Policy Exchange thinktank on Monday, the PM’s “integration tsar” Louise Casey blamed multicultural Britain, and political correctness, for the abuse of women – as if abuse never happened in the UK before Muslims arrived. Or maybe she believes, like Cameron does, that Muslim women are “traditionally submissive”.

The national press, as ever, is keen to fuel these stories: Casey was given a column in the Sun based on her speech; and the Times ran a news report quoting Trevor Phillips’ comments at the same Policy Exchange meeting, headlined: “Muslims are not like us, race equality chief says”. In fact, most of what Phillips said was commendable: “Part of the integration process is for the rest of us to grasp that people aren’t going to change their views simply because we are constantly telling them that basically they should be like us.” The headline writers instead chose more divisive words.

Cameron’s dog-whistles matter. They may appear to be mere words – jokes or slips of the tongue; but they set the parameters and the tone of the debate. We could call this trickle-down hate. So if he makes a bold statement about the niqab, or some other aspect of multicultural Britain, it will go to the top of the news agenda, even if it’s in actual fact insignificant or completely wrong – as in the so-called Trojan Horse scandal in Birmingham schools, which a parliamentary committee inquiry ruled to be groundless.

When, last year, two black passengers in separate incidents launched into a tirade of abuse against Muslims travelling on a bus, it was not just their race and the ferocity of the attacks that was alarming, but the fact they could recite so many Islamophobic tropes – from grooming, to terrorism, to FGM, to forced marriage. All important issues, of course, but all had been reported as if they undermine Islam itself and its billion followers, rather than being stories of individual wrongdoing.

And today we saw another consequence of this, with a rise in hate crimes on British railways – up 37% in five years. This confirms a trend seen last year, when there was a 43% increase in religious hate crime, and a 15% rise in race hate over the previous 12 months.

Cameron speaks; his entourage pushes further; the media responds; and on the streets, the abuse and attacks kick off. Sadly, Cameron and the Tories seem to believe that the answer to a broken nation is to break it some more.