Those who cherish the notion that the current prime minister really is ‘electoral Viagra’ should have paid a visit to Brixton last Friday evening to see what actual young people think about him. Before Slowthai — the young rapper from Northampton who ignored complaints about the toxification of political discourse by brandishing a dummy of Johnson’s severed head at this year’s Mercury Prize ceremony — even took to the stage, the 5,000 or so kids took up a chant of their own volition: ‘Fuck Boris! Fuck Boris!’

The Britain of Slowthai and his fans is not one in which anything can be overcome with a bit of Dunkirk spirit. The smell of weed, that eternal signifier of boundless ambition, hung heavy over the stalls (he introduced ‘Drug Dealer’ by asking ‘Who knows a drug dealer?’ It sounded as though everyone present did), and the title of the album for which he was nominated for the Mercury, Nothing Great About Britain, doesn’t burst with optimism. But this wasn’t a show that held menace or threat, necessarily. Instead, there was a sense of celebration and joy, from star and crowd alike (the crowd, moshing from start to finish and from front to back, was the most febrile I’ve seen in an age). ‘Do you know why these mirrors are here?’ he asked, gesturing to the reflective box that was the stage set. ‘They’re to show you how cool I look from the back.’ He laughed. ‘No, they’re to show you there is something great about Britain.’ For all the despair of his lyrics, it was, as the hashtags say, inclusive and relatable.

And the lyrics are terrific. Slowthai is witty, clear-eyed, free of self-pity. ‘Northampton’s Child’, the most nakedly autobiographical of the songs performed, detailed his childhood as the son of a teenage mum, and how attractive criminality can be when opportunity never knocks: ‘Fell in love with a drug dealer/ Picked us up in a limousine/ I remember lights/ Like a movie scene/ Took mum to dazzling heights/ Where she deserves to be.’

A cursory reading suggests he’s glamourising a terrible life, but he’s really not, he’s recounting it. And it isn’t just the life of the estates; it’s the life of teenagers wherever they rub up against gangs. My son is a middle–class kid keen to avoid danger, but the other week he came home to tell us that he saw a kid he knew get stabbed on Primrose Hill because the stabber mistook him for someone he didn’t like. My son understands what Slowthai is on about, even if I very much hope his mum isn’t hanging around in limousines with drug dealers.

Rap, now, is where extremity lies. So what of the groups who were once considered the most extreme, those ploughing the outer furrows of experimental rock? Melt-Banana, a duo from Japan, have spent more than a quarter of a century creating outer-limits noise: mixing the punk sub-genre known as ‘grindcore’ (it is precisely as attractive and melodic as the name suggests) with electronics and elements taken from dance music. Their London show — packed to the rafters, though in a much smaller venue than Slowthai’s — was tremendous fun, but it felt awfully safe by comparison.

This was experimental music as a hermetically sealed world. Where Slowthai absolutely obviously wants to reach out, no matter how scary the lyrics or harsh the beats, Melt-Banana existed just for themselves and the few hundred people who had come to see them.

It was such a closed world that no outsider could possibly know which songs were ‘greatest hits’ and which were unwanted obscurities. Pretty much every single one of them was played at extreme speed, such speed that chord changes had passed before you registered them. In the middle there was a burst of songs so short — just seconds — that entire songs had passed before you registered them. And the volume! Good God, the volume.

These days, I take moulded earplugs, made for musicians, to gigs. I have never been so glad of them. I could feel the noise coming up through my feet. I could feel it in my chest. At one point — I am not making this up — I could feel it making my nostrils vibrate.

With earplugs in, I had a chance of hearing what melodies there were. Without them there was only an enormous roar, more akin to standing directly underneath a jumbo jet landing than watching a band. I appreciate that criticising a noise band for their volume is a bit like complaining about the wetness of water or the salinity of salt, but equally, what does one gain from noise so brutal it exists only as physical sensation? With Slowthai, the danger is social; he might yet change something. The only thing Melt-Banana will change is your hearing.