Sugababes, Scala, London <br></br>Sinead O'Connor, Shepherds Bush Empire, London

And they'll give you a Chinese burn for afters...

Here they come with their thumbs in their belts. They don't want anything you've got to give. They look through you like you don't exist. They're as intimidating as hell.

From Day One, there's been something deeply unnerving about Sugababes. In the video which accompanied the uncanny, old-before-their-years ennui of "Overload", back when they were still borderline jailbait, they stared blankly down the camera with glassy eyes, inscrutable but knowing, unimpressed, unimpressable.

Tonight is the Sugababes first "proper" gig (that is to say, with live vocals, not lip-synching). If they're feeling nervous, they're even better actresses than they are pop stars. Nonchalant cool is their speciality. In 2001, I saw them perform "Overload" at the gay Mardi Gras. They sat immobile on stools until, at a pre-arranged moment, they all crossed their legs.

It was the coolest thing I'd seen all year. Tonight's no different: no choreographed dance routines, just subtle synchronised hip-swivels. Now and then they swap places. That's it.

Mutya Buena, or Mutant, or Muttley, as she was doubtless called at school, is the one who's foxier than a warehouse full of unsold Basil Brush glove puppets. Oh, she can sing too, which helps. Keisha Buchanan is faintly Orville the Duck-like, but does a mean hi-speed rap and an immaculate soulful wail.

Heidi Range is the Scouse one, the ringer, parachuted in from the Atomic Kitten reject bin to replace the departed Siobhan Donaghy, and her presence still jars. Inexplicably, she gets to do most of the talking. Didn't they have another schoolfriend who could sing? (For that matter, what's Siobhan up to now?)

Sugababes, we're told by the dull and unimaginative, are "the girl group it's OK to like". Girl group? No. Girl gang? Yes. In a recent TV documentary, Keisha and Mutya revisited their former school, and in each corner and corridor, commented "I had a fight there... and a fight there... and another fight there..." (Probably because someone called her Mutant or Muttley.) They're an urban British Shangri-La's, and their collection of glorious pop songs – "Run For Cover", "Round Round", "Overload" – is already impressive (although I could live without the cover of Sting's "Shape Of My Heart"). "Stronger", Heidi tells us, is personal to her; so much so that they do it twice, the second time as a piano backed encore. I prefer "Freak Like Me", which would surely be the most post-modern record in existence – a cover version of a bootleg (Girls On Top's inspired collision of Adina Howard and Tubeway Army) – were it not for the fact that Soundhog have recently done the same in turn to the Babes, laying their vocal over a Mansun track and creating "Take It Easy Freak" (download it NOW).

In this world of Pop Stars: The Rivals and Fame Academy, Sugababes' untutored cool, natural insouciance and unfakeable chemistry makes them a national treasure.

They all come back in the end, don't they? Lapsed Catholics are only ever on holiday. Whereas a Protestant upbringing is one long, half-hearted, resigned preparation for eventual atheism, Catholicism gets its claws in deeper. Obviously, aside from the ritual and ceremony which so seduced Wilde, there is something attractive about any religion which allows you to do whatever the hell you like as long as you say sorry to a little old man in a wooden box, and do a few Hail Marys (the RC equivalent of Bart Simpson's blackboard lines: "I will not bury the new kid", "I will not sell miracle cures", etc).

Until recently, Sinead O'Connor was about as lapsed as they come (she famously tore up a photo of Pope John Paul II on Saturday Night Live). It was fairly predictable, then, that her return to the fold would be equally spectacular and extreme. In the spring of 1999, she was ordained as a priest by the Tridentine order of Mater Dei, a quasi-Catholic religious sect, and can now apparently call herself, should she so choose, Archdeacon Sinéad Mother Bernadette Maria O'Connor. (This should perhaps be viewed in the pinch-of-salt context that she has also described herself as a Rastafarian, and trained as a psychic medium).

A Catholic she may be, but Sinead does a damn good impression of the puritan aunt in Blackadder II, sitting on a spike and eating raw turnips. Signs on the wall warn us that the bar is closed for the first 45 minutes of the show "For Patrons' Comfort". As a result, I can't tell you whether her version of the traditional "Lord Franklin" is any good, and neither can anyone else, as we stampede as one in an exodus to the re-opened bar, many of us wearing false breasts and singing wassailing songs.

However, there are signs that Sinead's public persona as a humourless harridan, so brilliantly nailed by Clare Grogan on Father Ted, is beginning to thaw, and that the big scary dyke lady (who, incidentally, came out as a lesbian in 2000, only to recant and modify it to "bisexual") knows how to have a laugh after all.

Arching her arms to aid breathing, she jokes "Now I'm going to do some ballet for you", and repeatedly mocks her own accent with an exaggerated "tank you tank you tank you!" after each song. OK, it's not Bill Hicks, but these things are relative.

Sinead's latest album, Sean-Nos Nua, is a collection of Irish folk songs by Mr Trad Arr like "Molly Malone" and "My Lagan Love", and tonight's set is heavy on those and light on the hits ("Mandinka" or "I Want Your Hands On Me").

Her stage presence is natural to the point of non-existence, sharing private gags with her band and ambling shoeless like it's her living room. I've mentioned this in connection with Lamb recently, but there's a regrettable tendency among artists of the liberal-leaning, world music-friendly type to go onstage barefoot (how long, I ask, before we see Damon Albarn with his hairy plates out?). This isn't Woodstock. This is a theatre. Please show some respect.

That said, her voice can still raise the hackles of the most hairless head, and the a capella encore, "In This Heart", in which she is joined one-at-a-time by the female members of her band, including accordionist Sharon Shannon, who from this distance looks uncannily like that ridiculously gorgeous girl from the Orange ad who wishes cats could chase Alsatians up trees, is breathtaking.

Having already dispensed with her biggest hit earlier on, Sinead resists calls for "Nothing Compares 2 U" with a firm "No, because only a miserable cow would sing that". Sinead O'Connor, miserable cow? Mother Mary forbid.

s.price@independent.co.uk