Blondie, Kenwood House, London

On a sunny afternoon, in the rolling grounds of Kenwood House, picnickers amass. It's all terribly civilised – there's probably been a run on Hampstead's houmous stocks – but as my friend mutters as we pick our way through the hampers, "CBGBs it ain't".

Blondie's drummer, Clem Burke, apparently hasn't forgotten their punk roots; he's wearing a T-shirt emblazoned with the New York club's logo. Though you might argue that's now just as "commercial" as doing an English Heritage Picnic Concert.

When they begin playing, however, it becomes apparent that Blondie have still got it. A very tight band is fronted by the still ice-cool Debbie Harry. The voice, admittedly, isn't quite what it was – she leaves the higher notes on "Atomic" to the audience – but it's still got that glossy sweetness and a bit of a growl.

I saw an absolutely electrifying set by Blondie at Latitude a few years ago, and while this never reaches such heights (lazy park setting? tired after a tour?) there is still much to enjoy. After new material – which holds up well, even if it can't ignite a hit-hungry crowd – they do an obliging "best-of". From shimmying her way through "Maria" to a decent post-Atomic Kitten rehabilitation of "The Tide is High" and a fizzing "One Way or Another", there's plenty of sing-and-dance-along potential.

Harry even delivers a sultry "Rapture", complete with its original proto-rap. The only awkward moment is when she bellows "do PUNK ROCK"; looking at the crowd reclining in deckchairs, or shuffle-dancing like aunts at a wedding, this literally could not be any less punk rock.

"Heart of Glass" is saved till last, and there's no denying that, over 30 years after it was released, this still sounds like a perfect pop song and a wonderful way to end a set. Although it's not quite the end – they move into a snappy cover of Michael Jackson's "Don't Stop 'til You Get Enough". It seems like we haven't had enough of Blondie just yet.