To fully understand the hormone-fuelled hysteria of a One Direction gig, you have to start with the noise. A grotesque torrent of pitchy screams punctuates the 90-minute show, and to the visible shock of the O2’s security staff, it takes almost nothing to set these highly-fidgety fans off. Even the sight of Niall Horan’s fortysomething dad sends a ripple of squeals through the crowd. In the words of a bemused parent to my immediate left, “The world’s gone mad”.

The set-up tonight is surprisingly loose, and refreshingly unbefitting of a PG-rated arena show. The stage is haphazardly dressed with 30ft screens showing assorted cityscapes and bubblegum graphics; two guitarists, a drummer and a keyboard player set the pace, while Horan & co. amble freely around the set, whispering jokes to each other when it’s not their verse.
As music’s hottest financial property, these boys don’t need to bother with costume changes or choreography: after the perfectly-formed party-starting falsetto pop, their personalities automatically become the main attraction. Niall playfully towels sweat off the forehead of a guitarist, Harry stares intensely into the crowd, Zayn broods into the cameras, Liam performs microphone tricks and Louis does his best to shy away from the drama. As if to break some age-old boy band curse, Horan cracks out a guitar on ‘Back For You’, a song that boasts three of their names on the writing credits.
That said, the best part of this show is not the group hugs or the bum smacks or the mirrored platform that hoists One Direction window-washer style out over the crowd, but the bit in the middle of the set where they field questions from the audience in real time via-Twitter.
It’s oddly touching to see the five most fancied men on the planet succumb to silliness and embrace their status as performing monkeys, giving their fans whatever they ask for (in this case, a rendition of the theme song from The Fresh Prince Of Bel-Air).
Of course, it all makes sense to a generation who record absolutely everything on their smartphones, who know what Bobby Horan looks like but don’t recognise Fatman Scoop when it plays over the PA, and who tweet before they think.