Elvis Costello and Steve Nieve, Royal Festival Hall, London

Costello returns to 1977

Perhaps it's fitting that this penultimate date of Meltdown happens when temperatures have reached the equatorial. Aged Scots wit Ivor Cutler is the warm-up act, but fortunately in a cool way. Sporting baggy trousers and an orange hat with a yellow daisy stuck behind one ear, he moves slowly as a zen priest and delivers his haiku with measured splendour and not a little threat: "Pussy On The Mat," begins, "Lie down, pussy/ And I'll turn on the Hoover". Giddy with tales of blind men falling into canals and halibuts wooing albatrosses, a male voice shouts from the balcony, "I love you, Ivor!" Cutler beetles over his glasses. "Och, I'm the heterogeneous type," he warns, adding, "You've got to be a little bit nasty."

If heterogeneous means "composed of unrelated parts", it may be the way to describe Elvis Costello. Flagged in the programme as a "genre-busting genius", Costello has embraced eclecticism with dilettante-ish glee. From rock to country, through classical with the Brodsky Quartet and Weill with Ute Lemper, past cabaret with Burt Bacharach and a collaboration with mezzo-soprano Anne Sofie von Otter, he dabbles frantically.

He's earned the right having written some peerless, deeply moving songs. But has he written any lately? It's hard to tell: he's pushing the envelope, all right – problem is, it's an envelope you don't often want to open. His work seems less soulful, more like precision engineering, mannered and wilfully obscure. Is this stretching yourself or just self-indulgence? Certainly, Costello has moved toward cult status.

Tonight, as it turns out, has a big surprise up its sleeve, but we don't know that for the first hour, when the smaller surprise is that Costello has, this time out, turned into Fatboy Slim. Alone on the stage with Attractions pianist Steve Nieve, he takes his seat behind a bank of synths and drum machines, picks up a guitar and turns "Somebody's Gonna Get Hurt" into an extended mood piece, filled with tape loops, Echoplex and bizarre samples ("we're gonna try another side to these songs, see what we find").

This works, and works again on more, almost unrecognisable, numbers but, as deep house beats cascade and distant bells sound, with only the occasional lyric, it feels like sitting in on a radiophonic workshop and, well, I think he's getting away from us.

The Brodsky Quartet troop on for "Pills And Soap", a shocking American folk song, a Juliette Gréco-style chamber piece and a splendid reading of "New Lace Sleeves" – then he's back to the synths for numbers which are darkly anarchic but deeply distancing – there's emotion in there but it's lost in the random bleeping.

There's an arch "Shipbuilding" then, with the Brodskys, a rousing "Walking on Rockinghorse Road" and spartan "Almost Blue". And then, just when you think it's all over, the set starts being rebuilt and, in a haze of footstamping, Costello appears with the dusted-off Attractions, or at least Nieve and drummer Pete Thomas, with capable help on bass.

Delirious old fans pile down the front for a knees-up and blimey, it's just like 1977, with "Waiting for The End of the World", "Pump It Up", "Alison" and a cast of thousands. It seems he does care after all, handing out sugar lumps for those who've stayed the course. And thus the devious Costello, grinning like a ferret, triumphs again, drat him.