Blondie/Sly and the Family Stone, Lovebox Weekender, London

They were pioneers who became icons of popular music. But can Sly and Debbie still cut it at 60?

If you push a pistol to my temple and ask me to name the most perfect pop group of all time, I'm only ever gonna come up with one answer. I will tell you that Blondie are the absolute apex of pop as an art. One sassy and street-smart, devastatingly, atomically attractive woman with plutonium blonde hair, feline cheekbones and calculating eyes. Five guys in skinny suits who called time on rock's decade-long bender of indulgence and pomposity and returned to pre-1966 imperatives of conciseness and melody. And a multitude of hits which are from one angle brilliantly blank, from another, deliciously deep. It simply doesn't get any better than that.

The best way to experience the most perfect pop group of all time, however, probably isn't in a London park surrounded by tan-skinned twentysomethings whose hair smells of cannabis and who are only here at the Lovebox Weekender to kill time before the Rip Curl Boardmasters festival in Newquay ("Oh mate, it'll be suu-perb!"), drowning out the music with their chatter. You'd think that if dance act Groove Armada, Lovebox's organisers, could get anything right, it would be installing a huge sound system, but you'd be wrong.

Debbie Harry was, I'm fairly sure, the first person I ever fancied. The thing which appealed was the cute way her top and bottom teeth didn't quite match, and she'd grind her jaw from side to side when she smiled. At the age of 62, the jaw-grinding thing is pretty much all that remains, even if, with her Hillary Clinton hair and diagonal-striped dress, she's gained a certain Mrs Robinson factor. As she peers from behind her dark glasses, I wonder what she's thinking.

There may be a ferris wheel overhead, but Victoria Park ain't Coney Island. She must wonder: has it come to this? Close your eyes and swoon to "Union City Blue", and you can just about dream that this is the Lower East Side, not the upper East End. But I want to see Harry, Destri, Stein and Burke dominating their context, not subservient to it. Next time, make it a 1,000 capacity club show. As long as I'm invited.

By the time Sly and the Family Stone take the stage, I'm at the top of the ferris wheel. At first, I'm not missing much. After 10 minutes of jazz-funk noodling, a familiar thumping beat kicks in and a large lady begins singing stage-right. This, obviously, isn't Sly Stone: it's his sister, Rose. She's joined, stage left, by a gentleman whirling, dervishly, in a white robe. This isn't Sly either: it's singer Fred Ross. The Family Stone, in 2007, literally is a family affair: the siblings, and in some cases the children, of the 1960s-70s band.

Four decades ago, they were a family in a far more subversive sense: black and white, male and female, a gender and race-transgressing collective, a concept which was as revolutionary at the time as the melting-pot psychedelic soul sound they pioneered. Having done a phenomenal amount of drugs, even by Sixties standards (the afro-haired leader was known to carry around a violin case filled with cocaine and angel dust), the band split in 1975. But not before leaving behind some exquisite records and arguably inventing Seventies black music (no Larry Graham's slap bass = no Bootsy Collins, no Bootsy = no funk).

Since the split, Sly has been one of rock's most famous recluses, making only fleeting returns to music. This year's tour is one of them, and even then, it's 20 minutes before he staggers on, a hunched figure in a hood, hat, shades and a gold chain.

Sitting down at a keyboard he doesn't actually play (the overhead handclaps are the giveaway), he performs a slowed-down, almost lobotomised version of "If You Want Me to Stay" which lacks any of the sexual menace of the record, and you start to realise how damaged he must now be.

He sticks around for "Stand" and "I Wanna Take You Higher", randomly hitting things with a drumstick or fiddling irrelevantly with a keyboard until he gets bored, then wanders off while the Family Stone play on. You thought Brian Wilson was a decrepit passenger in his own band? Compared to Sly Stone, Brian Wilson is Iggy bleeding Pop.

I later work out that Sly Stone is one year older than Debbie Harry. A year is a long time, when you're carrying a violin case.