Rock: Very good at being themselves

Portishead Is not just the name of a band. It's the name of that band's second album, and it's the name of their hometown, just outside Bristol (the show in the Brixton Academy on Wednesday began with "Welcome to Portishead" signs flickering on the backdrop), a town which must have mixed feelings about losing its identity to the renowned pioneers of post- hip-hop haunted-house lounge music.

A few seconds into the gig and it was clear that Portishead is also the name of a genre. You may (at your own risk) call the band trip-hoppers, and you may compare them with Massive Attack or Moloko, but no one makes music like Portishead do. No one else can evoke desolation and anguish in a way that is so classic but so revolutionary, and so spine-chilling that it makes passing Goths tear their black hair out by its blond roots. Portishead are a genre unto themselves - and that's why they are so important. If you see only one gig this year, then you should really get out more often; if you see only five gigs this year, Portishead's should be one of them.

In concert, Portishead the band do Portishead the genre as impeccably and stylishly as they do on Portishead the album. Projected on to the backdrop are oily tendrils of smoke, then a haze of television interference, then a green wave-pattern which responds to Beth Gibbons's vocals: as her spiky Germanic caw gives way to a pure, desolate cry, the line trembles, then spasms into jagged peaks and troughs, and you wonder why no one else came up with this idea before.

Gibbons' voice - so icy that the people at the front of the crowd had to wear mittens - is complemented by shivers of organ, alien cackles from Geoff Barrow's record decks, and Adrian Utley's diverse, but always stately and economical guitar. Each band member is intensely focused on making sure that Portishead never get a Christmas number one single. They know precisely what they're doing.

Sometimes this can be frustrating. Portishead have mastered a particular mood, and show no signs of venturing into another genre, so you know from the first few bars how the whole concert will sound (Portishead is a fabulous place to visit, but I wouldn't want to live there). These self-imposed limits may explain why the band struggled for three fraught years between the first album and its follow-up. When I saw Portishead on their last tour I wondered how they could possibly make a second album; this time I wondered how they could possibly make a third.

If the stuff that Shaun Ryder writes weren't bad enough, you should read the stuff that other people write about it. He is now so treasured as a roguish British institution that educated journalists have feted the couplet, "I wanna get cheeky with you / I wanna get squeaky inside you," as the boldly unflinching work of a trail-blazing new voice in British poetry. You can't blame Ryder for this. He called the new Black Grape album Stupid Stupid Stupid (Radioactive), for goodness' sake, so what else is he supposed to do before the hermeneutics professors get the message - name his next album No, Really, This Is Just a Load of Nonsense Off the Top of My Head?

Black Grape recognise that those of us with busy, high-pressure, executive Nineties lifestyles don't always have the time to murder our favourite songs by shouting rude rewrites of the lyrics after the pubs close. The band deliver the songs to us pre-murdered, pre-shouted and pre-rude (at the tube station after Thursday's gig, an Australian was heard to complain, "That guy can't hold a tune to save his life," which was missing the point by a light year or two). But at the Kilburn National, the band were too murderous for their own good, and the multi-layered, effects-laden, head- inside-a-pinball machine zing of their CDs was bludgeoned into bleary, workaday funk-rock.

The musicians seemed well-drilled, so the problem may have been the sludgy mixing; it may have been the absence of Danny Saber, the producer and multi-instrumentalist who more or less is Black Grape on the records; or it may have been just the lethargy of the Three Unwise Men who front the band. I don't know if Ryder had taken too many drugs or too few, but he could have passed for a punch-drunk ex- boxer, hauled out of retirement for one last fight, slipping in and out of consciousness. Carl "Psycho" McCarthy moped around the stage like a sulky child - presumably the person who gave him his nickname also calls short people "Lofty" - and Paul "Kermit" Leveridge didn't live up to the grandstanding charisma of his recorded self either. I never thought I'd miss Bez.

During the encore of M People's show at the Birmingham NEC last Friday, Shovell, the Popeye lookalike who plays percussion, was allowed out from behind his bongos to whip up the crowd with his chatter. He did so five times as well as Mike Pickering had done for the rest of the concert, which may be why Pickering, the band leader, usually keeps Shovell away from the mic. Pickering is 41 (and he dances like a 41-year-old), but he still hasn't grasped the finer points of rabble-rousing. Earlier, he had promised the audience, with no trace of irony, that "if you have half as much fun as we do tonight, you're gonna be ... satisfied." Well, don't get us all over-excited there, Mike.

The first half of the show drew from M People's thoughtful new album, Fresco (BMG), which is probably why the audience came to life only for the second half. You could say that the band were right not to allow their back catalogue to hold them back, but I was on the side of the people, not the People. The songs which mark the mature new direction aren't actually more insightful or moving than the disco favourites, they're just fractionally slower and less catchy. There is no doubt that Heather Small's gargling voice is unique - whether you think it's a thing of beauty, or whether it makes you want to shout, "Don't sing with your mouth full," is a matter of personal preference - but it doesn't vary from song to song. She expresses no emotion, and, likewise, the musicians behind her don't seem clear whether their songs are happy, sad or somewhere in between.

Small has finally given up that coiffure which made her look as if she were balancing a pineapple on her head, but figuratively speaking M People haven't let their hair down: there was no spark of wit or spontaneity. Maybe they should have gone for an all-out party atmosphere and had done with it. As it was, I think Pickering was right. The audience were satisfied, and they did have half as much fun as the band.

Black Grape: Poole Arts Ctr, 01202 685222, tonight; Norwich UEA, 01603 505401, Mon; Cambridge Corn Exchange, 01223 357851, Tues; Nottingham Rock City, 0115 9412544, Wed; Middlesbrough Town Hall, 01642 245432, Fri; Glasgow Barrowlands, 0141 552 4601, Sat; Doncaster Dome, 01302 370777, Sun 7 Dec. M People: Newcastle Arena, 0191 401 8000, Mon; Hull Arena, 01482 325252, Tues; Glasgow SECC, 0141 248 9999, Thurs & Fri; Aberdeen Exhibition Ctr, 01224 620011, Sat; and touring.