Rage Against the Machine, Finsbury Park, London<br/>Bon Jovi, O2, London

While Rage Against the Machine bring their political rap rock to London, Bon Jovi hark back to their poodle-permed past

The political pop lyric can succeed in many moods and modes, from withering accusation to thoughtful reflection, from righteous fury to quiet dignity, but one that never, ever works is petulance.

Rage Against the Machine's "Killing in the Name", the 1992 single that became a surprise Christmas No 1 in 2009 after a Facebook campaign helped it to outsell The X Factor winner Joe McElderry, is an explosive rant against racism in the armed forces. Its famously sweary refrain is all too easy to traduce as "Fuck you, I won't tidy my bedroom". And I'm usually the first to do so.

However, I was also the first Brit to interview RATM on its original release, and I remember being bowled over by the articulacy of Harvard-educated Tom Morello. In the intervening years, Rage's musical style – rap rock – has gone in and out of fashion at least twice, but none the less, Morello has assumed the mantle of American alt-rock's radical conscience: his generation's Jello Biafra.

The Rage Factor, a free concert to thank Britain for the bizarre chart-topper, is London's first big outdoor happening of the summer, and the band certainly haven't toned down the politics for their new mass audience. Their set is prefaced by an unsettling KKK speech referring to the "destruction of the inferior nigger race", lifted from Apocalypse 91 by Public Enemy, whose own "Shut 'Em Down" follows. The event is noticeably free of corporate branding, with only the red and black stars of socialism and anarchism on display.

According to the official T-shirts (Rage 1 Cowell 0), this is a "victory celebration", and RATM's arrival is heralded by an animated Simon Cowell, crowing "I'm the biggest star maker in the world ..." to two minutes of booing. After a blistering "Testify", Zack de la Rocha's first words to the 40,000 lucky attendees are: "They weren't ready for you at Christmas time, ha-haa ...", delivered with a Nelson Muntz cackle.

Rage may be a one-trick pony, but it's one hell of a trick, and in terms of sheer incendiary detonations, the band leave funk-metal peers like Red Hot Chili Peppers standing. It helps that Morello's an unashamed guitar geek, who boasts of creating crazy sound effects with his fingertips and without recourse to pedals. On "Know Your Enemy" his fretboard is a police siren. On "Bulls on Parade" it's a violin and a scritchy-scratchy turntable.

After a week when Israel has been acting the school bully, De la Rocha dedicates "Township Rebellion" to "all the brothers and sisters from Nablus, the West Bank and Gaza". These are sentiments to which the average Kerrang! kid is not exposed at the average Lamb of God gig, and for that alone Rage are priceless.

After "Bombtrack", I notice a trickle of break-ins arriving via a conveniently placed tree behind the back fence, which turns into a human tide during "Bullet in the Head" when the fence is kicked down and the 40,000 crowd probably doubles. It only adds to the excitement under the drizzle.

A mere six years separate their respective breakthroughs, but Bon Jovi and Rage Against the Machine seem aeons apart in metallic terms. The verse "Tommy used to work on the dock/Union been on strike, he's down on his luck/It's tough, so tough ..." from Jovi's "Livin' on a Prayer" always used to make we wanna scream: "Yeah, Jonbon, well maybe the union's been on strike so that thousands of people like Tommy don't have it so tough in future, you Reaganite dimwit." It turns out, however, that Jonbon's a celebrity Democrat who's raised millions for their campaigns. He just doesn't get the whole "organised labour" thing.

The hair metal era was cut short by grunge, and so, literally, was the metallers' hair. None more publicly than Bon Jovi, who forsook their poodle perms in a public act of repentance.

Fashion has since turned full circle. Everyone's realised how much fun you can have punching the air to "You Give Love a Bad Name", and it's unrepentant poodle rock that everyone wants to hear. Bon Jovi are essentially Springsteen for babies, Springsteen after the Hollywood test-screening audience have tacked on the happy ending. And, like any metal band, they sell a "gang" myth. Guitarist Richie Sambora, whose silly "woh-woh" voice synth is exceeded in ridiculousness only by his double-headed acoustic guitar, shares a bromance with JBJ that borders on the homo-erotic.

To make it clear just how hetero he is, the singer advances on to a crescent-shaped catwalk to serenade the ladies with "Bed of Roses". It's pure New Jersey cheddar, but you can't help grinning along. Then I notice something poignant. He isn't looking them in the eye. Instead, Jonbon's gaze is fixed on a string of autocue screens.

He's been everywhere, and he's standing small. He's written a million lyrics. And he's forgotten them all.

Next Week:

Simon Price sees if Scissor Sisters are still an infallible hit machine