Television's most toasted crumpet has the gravitational pull of a medium-sized planet. A Soave-swigging, chain-smoking, drug-taking, long-legged sexual adventuress, she storms through life, scattering empty bottles, full ashtrays and crumpled conquests in her wake. She is a very tough cookie.

But she is also a dope cookie. Anna's worst enemy is Anna. Her high intelligence is matched only by her low common sense. Every time she takes two stilettoed-steps forward she takes another one back - towards the sign saying 'completely off the rails.'

Anna's impoverished Glaswegian background - 'my father left when I was eleven: my mother went to bed with a packet of Tamazepan' - is the cause of her insecurity. On the one hand, it made her hugely ambitious to escape. On the other, it sowed the seeds of self-destruction. She buys Ecstasy from a dealer - and has to defend him in court the next day. She is sent to Alcoholics Anonymous - and then gets trashed. She fights like mad to get her tenancy - and nearly throws it all away by snorting coke in the loo. But here, with a tenner up her nose and her life collapsing all around her, is the essential appeal of Anna. She's vulnerable. Underneath the sassy, brassy, sexy, strident siren is a lost little girl who wants her mum. But she can't have her. Although Anna greets the news of her mother's death with stunning indifference, we know - and then we see - that the indifference is a fa­ade. And when that facade collapses it's both shocking and heart-rending. The sight of a drunken Anna, weeping in a sea of spilt wine and broken glass, is one of the starkest images and most poignant moments of This Life.

Her relationship with Miles best defines the seething mass of contradictions that is Anna. She wants him but she can't have him, so she scatters banana skins over the rocky terrain of their relationship. One minute she is climbing into a wardrobe with him - the next she's throwing a pint in his face.

She's good at throwing spanners in other works as well: apart from doing her best to scupper her career, she almost ruins the terrific friendship she has with Milly - a friendship that shows Anna at her witty, outrageous, generous, loyal and fiercely protective best. She and Milly couldn't be more different - 'I'm bad fairy. You're sugar plum' - but the friendship works because of, rather than in spite of those differences. There's no competition between them.

But there's competition in every other area of Anna's life - and at work in particular. She will consider pretty much anything in order to further her career: she samples a Sapphic snog, sleeps with the clerk, butters up the boss and bullies the opposition. This ought to make her into a monster, a rapacious amoral slut - yet because she's so up front about everything it just makes her moreŸmore Anna. As Miles says to her of the beautiful, barmy heroine of the film Betty Blue, 'She was a headcase - but she was worth it.'