As glitter falls from the rafters on to the stage at Hoxton Hall, Jessie Wallace, dressed and rouged up as the music hall legend Marie Lloyd, sings a mournful song about wanting “a little bit o’ luxury”. She’s wearing a billowing Victorian silk dress, a corset with super-boob uplift and a tiara studded with stars on little sticks. Later, in a lime-green coat, glitter still in her hair, Wallace visits our band of cold, bored journalists as we eat lunch on the top deck of a specially rented bus.

We ask her about playing Lloyd. It’s “great”. We desultorily pick over Lloyd’s life: the messy love affairs, the public adulation, the fall from fame, the tabloid disgrace. Ring any bells, we ask Wallace as politely as possible. No, she says. She so doesn’t want to be here. We ask Wallace about Kat Slater, the EastEnders character that made her famous. She’s “moved on”, she says granite-faced. The temperature drops a thousand degrees. We go back to the remains of our lunch.

Later, one-on-one, Wallace explains that she hates “raking over old stuff”: “I just want to let it go. I wish people would let me do that.” She’d rather talk about playing Lloyd, or her role in the BBC One drama A Class Apart, for which she got moderately warm reviews playing the mother of a gifted working-class boy.

The problem for Wallace is that she played one of the all-time great EastEnders characters, the leopard-print wearing scrubber made good, the tart with a thudding heart. Kat roared like a banshee and bled like a true soap diva, all the time decked out in vertiginous stilettos and heavy kohl make-up. Kat sold her body, she lost everything, and then finally married her one true love, Alfie Moon — she was a cartoon queen in the grand tradition of Coronation Street’s Bet Lynch.

And just as with Julie Goodyear, who played Lynch, reality and fiction started to merge. Kat’s tumult of melodrama onscreen was matched by Wallace’s dramas off. She allegedly slapped her co-star Hannah Waterman — who played the EastEnders character Laura Beale — during a row at a BBC party (Wallace admits a row but denies the slap). A Muslim mini-cab driver accused her of hitting him and calling him “bin Laden”. She was suspended from the show and arrested after drink-driving.

Last year she confessed to out-of-control boozing and a drug habit after Dave Morgan, an ex-boyfriend and the father of her two-year-old daughter Tallulah, went public on their volatile relationship.

Wallace calls him a “parasite” today — and that goes for “all the others” who have sold stories about her to the papers. “The crap that I’ve let into my life . . . ,” she says. “These people had one thing in mind — to earn money from me — and I do think it is quite disgusting that they were paid for their hideous stories. If you believed half the things written about me — like I was about to have some tranny’s baby . . .”

Is she on speaking terms with Morgan? Eek. If looks could kill. “He. That. It. . . doesn’t even come into the picture. He got his fistful of dollars. That’s all he wanted. I’ve done nothing wrong— I’ve moved on. I’m a better, stronger person. I’ve got this fantastic career.”

Wallace repeats this positive mantra again and again. She is desperate to leave Kat and her lurid public image behind. Kat’s raucous laugh might still be there, but Wallace is dressed in ethnicky clothing and gone is Kat’s alarming orange tan.

She is newly blonde. “I wanted to have a completely different look to Kat,” she says. It must feel odd, because since Kat she seems to have got stuck in the groove of playing tough but tender East End heroines, just like Kat, first in A Class Apart and now with Lloyd. “I think it will take a while for people to see me differently,” Wallace admits. “But six million viewers watched A Class Apart and I’ve had nice comments from people. If critics want to compare all working-class London women to me and Kat, that’s fine. But yes, bring on the different parts.”

Wallace, 35, wanted to be an actress since she was a young girl . At her grandmother’s she watched old movies starring Joan Crawford and Rosalind Russell, and was transfixed by their glamour.

Her parents broke up when she was 3 and she lived with her father. “I was terrible at school, very naughty — something I’m not going to allow my little girl to be. I used to play truant. Me and my friends would take our own clothes to school, get changed in the loos and take a bus to Trafalgar Square. I hated authority. Looking back, I wish I could have done things differently but it’s what’s made me the person I am.”

Her father tried and failed to discipline her. A teacher once found her reading a glossy magazine while in detention. “She grabbed it out of my hand and said, ‘You expect everything to fall into your lap.’ I’ve never forgotten that. She was right — I did. How wrong was I?”

But eventually, everything did fall into place. Wallace really has done it her way. From 15 to 22, she had a succession of “deadend jobs” in bars and kitchens. She “got to the point where I was like, ‘This is ridiculous, what am I going to do with my life?’ ” She enrolled in a theatrical make-up course and got a job at the Royal Shakespeare Company. “I would watch the actors and think, ‘That’s what I want to do.’ ” Iain Glen and David Tennant helped her to fill out her application to the Poor School. To her amazement she got in. It was her drama coach, she says, who realised that she had something and likened harnessing her talent to breaking an egg. Early on she took on roles “like a cloak you put on”. Later she realised that she had to generate the characters from within.

Wallace didn’t work for a year, then got a small part in The Bill before attending an EastEndersworkshop: the producers were looking to cast a family of sisters that would go on to become the Slaters. “I never wanted fame or celebrity,” she insists. “It spiralled out of control.”

Here her life mirrors Lloyd’s. She became fascinated by her new role: she had to find three different musical voices for it, a Cockney speaking voice and a “mock-posh” one. “The fact that she was a woman doing her own thing [Lloyd’s suggestive songs fell foul of the authorities] was impressive.”

The most difficult scene to film, says Wallace, was Lloyd’s death. On October 4, 1922, during a performance of the last song in her act, I’m One of the Ruins that Cromwell Knocked About a Bit, Lloyd staggered about on stage. The audience assumed it was part of the act. But she was seriously ill and died three days later. In the BBC film, she dies on stage. “I was completely delirious by the end of filming,” says Wallace. “I was saying goodbye to her. There were 120,000 people at her funeral. What a life she had. She married three times. She started a strike at the music hall. And she was spattered across the press a few times.” This is accompanied by a roll of recognition in Wallace’s eyes.

What’s that like, I ask. “Betrayal is the worst thing. As soon as you realise someone is feeding off you, you turn your back on them. Then they think they’re not going to get anything else out of you so they think, ‘Right, I’ll just go the whole hog and take the final big chunk out of your a*** [by going to the tabloids].’ ” She laughs. “Generosity was my downfall. Now my barriers are up.”

She is not seeing anyone nor is she is interested in doing so. It’s work, work, work: a new drama for the BBC is in the offing and she is “desperate” to start a theatrical career — Nancy in Oliver, Blanche in A Streetcar Named Desire and “any Restoration play” would be dream stage roles. She doesn’t feel she has “the right face” for Hollywood (unlike Michelle Ryan, who played her screen daughter Zoe, and who is to play the Bionic Woman). “But of course I’d love to go to Hollywood. Any actor who says they wouldn’t is lying.”

Over and over again she emphasises that the Wallace of popular lore — potty-mouted, falling out of night-clubs, chaotic love life — is no more. She “likes a drink”, but that’s all. “I’m a mother,” she says more than once in a glassy Walford to Stepford tone.

“It’s overwhelming, the love you feel.” A lot has been written about her fluctuating weight but she laughs it off. She’s tried every diet and now just tries to eat healthily. She used to be horrified watching herself as Kat “looking like Danny DeVito”. But the running machine at home remains unused. She walks the dogs. She relies on her best mate Nikki and her dad for advice.

As well as all the endless mantra-spouting, the other thing Wallace keeps saying is, “I don’t really care any more.” Is it a positive, I’ll-do-as-I-please not caring, or more resigned? “If I think someone doesn’t like me, before I would have been worried about it and wondering why, now it’s like, ‘Whatever’. Before I was really insecure. Having a lot of s*** has changed me.” As in, made her harder? “Not too hard, no,” she says, very earnestly. “I’m not unbreakable but nothing fazes me now. Do you think that’s a bad thing?” She hates talking like this, it’s the closest she’s come to therapy she roars, mortified. “You wear your heart on your sleeve and you say things you don’t want to say. When it’s in print I can look like such a t***. That’s my worry.”

What’s the biggest misapprehension about her that people might have? She says very precisely and without pausing: “That I’m feisty and that I can be quite nasty. I’m neither.” So she isn’t Kat, but the bits of Kat she does have — the self-possessed chippiness, that laugh — are pronounced, hence the confusion between actress and role. Hurry up, casting agents, and find her a lab coat and a melting ice cap to save.

Miss Marie Lloyd: The Queen of the Music Hall, Wed, BBC Four, 9pm

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