M.I.A, Brixton Academy, London

Well, this was unusual: a woman in a burka entering a dingy, beery rock venue.

As the sort of women who wear burkas are unlikely to frequent places such as Brixton Academy, at least not when they’re full of people of both sexes mingling and drinking alcohol and listening to very loud music, it was fair to assume the outfit was fancy dress. Lady Gaga’s fans wear lightning-bolt make-up, Madonna’s fans wear pink cowboy hats; M.I.A’s fans wear burkas.

Maya “M.I.A” Arulpragasam is one of pop’s most electrifying provocateurs. Although small fry sales-wise compared to Gaga or Madonna, she’s stirred up her fair share of controversy. Invariably it’s because of her politics, some of which is daftly conspiratorial – her latest album, Maya, opens with the dopey insinuation that Google is a form of government surveillance – but much of which is genuinely bold.

Her biggest hit, “Paper Planes”, was an ode to third world criminality set to playground chants, the sound of cash tills ringing and gunshots. MTV edited out the gunshots, but it still sold more than 3m copies in the US. This year, YouTube temporarily removed a video to one of her songs that depicted a Swat team rampaging through the US as if in a war zone.

M.I.A ascribes the violence of her songs to her refugee upbringing: the daughter of a Tamil activist, she fled Sri Lanka with her family during the 1980s civil war to live in London. Critics dismiss her as the 2000s equivalent of 1960s radical chic, showing a phoney solidarity with the wretched of the earth from a position of great comfort: the 35-year-old currently lives in LA where she’s married to the wealthy son of a major record label mogul.

Squeamishness about M.I.A’s mix of pop and politics misses the point. It’s better to think of her as an expert in shock tactics, learnt when she was a student at art school in London in the 1990s: a time when sensation-seeking Brit Art took over pop’s traditional role, outraging respectable opinion.

At her best, M.I.A in concert is a breathtaking experience with arresting visuals, adrenalin-fuelled beats, reverberating bass lines and a collision of different cultures: hip-hop, Indian temple music, rave, Brazilian funk. It was therefore a grave disappointment to find she was nowhere near her best at Brixton Academy.

Opening number “Illygirl” found her, true to form, rhyming “Bruce Springsteen” and “Mujahideen” while wearing sunglasses, bright red lipstick and a keffiyeh, the Arab headdress favoured by the Palestine Liberation Organisation. But the sound was muddy and oddly sluggish. Occasionally songs snapped into focus, as with the lithe Missy Elliott-style bounce of “Galang”, but too often the creative chaos of her music tipped into incoherence, symbolised by gloomy stage lighting and virtually indiscernible vocals.

The shortness of the set, barely an hour long, was exacerbated by pauses between songs as M.I.A fiddled with controls at a podium or swigged water. The sense of deflation was summed up by “Lovalot”, in which the singer announced “I really love Allah” as men in Arab dress paraded behind her. It should have been provocative; instead muffled beats and the singer’s indifferent delivery conspired to make it merely routine. Her boldness of vision is undoubted, but tonight it wasn’t matched by boldness of execution.