Fresh Meat's Zawe Ashton, AKA Vod, is the coolest thing on TV right now

Television's coolest characters often come with a signature "thing". The Fonz from Happy Days had his leather jacket and his thumbs. Master William from The Fresh Prince Of Bel-Air had his hi-top fade and loud trousers. In the Channel 4 comedy Fresh Meat, Vod has her off-the-wall clothes and that withering gaze that cuts down foolishness at 20 paces. She's easily the coolest character on television at the moment, but when I tell that to the woman who plays her, the response is charmingly modest. "I would really like to keep anyone who says that in my pocket, as I go about my daily life," says Zawe Ashton (the Zawe is pronounced like "Bowie"). "When I hit a low point, I'd just ask, 'What's that you're saying in there? I'm the coolest person on TV? OK, I'll take that!'"

With the third season of the show starting on Monday, it feels fair to say that Ashton is the breakout star of Fresh Meat. Her many memorable moments include preparing coq au vin with a sword (at posh boy JP's family home) and a lecture-hall monologue about Salman Rushdie's Midnight's Children ("I feel like I've got this pompous, fat, naked man sitting on my face, and he's resting his big, overrated bollocks on my airways"). She is the show's wry centre, looking askance at the dubious decisions made by her housemates and doling out wisdom as necessary. The character works best in concert with the others, though, and the ensemble is excellent, something Ashton puts down to a meticulous casting process and a writing team who really understand the characters. "Everyone in this show was put through a very rigorous process," she says, "and I think that's real testament to Sam and Jesse [Bain and Armstrong, the show's creators]. They were determined to find a group that worked together, and not just go, 'Who's hot right now?'"

In person, Ashton is only superficially like her plain-speaking, no-holds-barred alter ego: her speaking voice is slightly less deep, far less estuary than Vod's, and she's clearly more prone to both chuckling and thinking before speaking. The source of Vod's cool – The Essence Of Vod, if you will – can be boiled down to a simple but powerful philosophy: she doesn't care what anyone thinks. "I always describe her as having no subtext, no filters," says Ashton. Combined with the fact that she's a girl – and a black girl at that, which is almost never brought up as an issue to be "tackled" – Vod was primed for cult status from the start.

"The door has felt very open in terms of the interpretation of Vod," continues Ashton. "I've never had to take into consideration any external factors, I've been able to find out who this girl is from the inside out." The lack of extra racial baggage has paid dividends – last November she won a Creative Diversity Network Award for her performance, with the board praising Vod as a great example of racial diversity on our screens that didn't come served with a side-order of self-congratulation. "That was so moving for me, because I do think about these things. I'm not the kind of actor who blocks out the undertones of the industry. I've been acting on TV since I was six, so 23 years would be a long time to keep your eyes averted." She arches an eyebrow.

Let's talk about those eyebrows. And lips, and clothes. Where on earth does Vod shop? And how hard is it for Ashton to "become" her? She laughs again. "I'm telling you, once the head was shaved and the dummy was round the neck and the leather jacket and bovver boots were on, it was like, OK, we're ready. The whole birth of that character was so much about hair and makeup and wardrobe. RiRi's only just catching up to the dark blue lip!" She gives high praise to Janet Horsfield and June Nevin who head the makeup and wardrobe departments. "They're so collaborative in the process. I was cast the day before we moved to Manchester. I literally got there and was like, 'This is who I think she is – is that all right?' and they just worked in record time and completely understood what all the references were." Like what? "We imagined what her parents listened to musically: a lot of Bowie, dancehall, ska. Plus I feel like her nan had a lot of influence over how she grew up because she's never been close to her mum or dad. Sometimes Vod dresses like an old man, and I feel like she's kind of empathising with her grandparents. She's a forager."

We gain an insight into Vod's mysterious background in an upcoming episode, when her mum comes to visit. "It's another layer to Vod. [Writer] Penny Skinner met up with me before series three started, and said, 'Look, I really want to write something for Vod. We need something from her past, some kind of key to her upbringing to continue that identification that audiences are having.' I just went, 'Thank you, let's do it.' And the result deepened my empathy for her." The character of Vod has evolved over the series and the process, Ashton thinks, has been organic and natural, the big change being that she's now formed real bonds with her housemates. "I don't imagine she lets people in very easily," Ashton says. "I think Vod is a sage. If she gives you some serious insight into your life, you're going to consider it. Because those nuggets come few and far between, but when they do come, they land."

Ashton's parents still live in the east London house where she was raised, the eldest of three children. Her mother Victoria emigrated to the UK from Uganda as a teenager. She became a teacher and married fellow educator Paul, an Englishman who later worked for Channel 4 in educational programming. Victoria encouraged her daughter into drama and she attended the famous Anna Scher school from the age of five. Childhood roles in Desmond's and The Demon Headmaster were followed by parts in Holby City, Casualty and the St Trinian's sequel. Since then, she's popped up in BBC1's Case Histories (as Jackson Brodie's assistant Deborah) and E4's Misfits (as a virgin with an overprotective killer dad). Most notable of all, however, was her performance in Carol Morley's film Dreams Of A Life; Ashton was nominated for a British Independent Film Award for her portrayal of Joyce Vincent, a woman whose lonely death went unnoticed for three years.

Ashton is more than an actor, too. In 2000 she won the London Poetry Slam Championships, while her play Harm's Way was performed at The Lowry in Salford and nominated for the Verity Bargate award for new writing in 2007. She has just written and directed a short for BBC Films, Happy Toys. "They approached me because of Fresh Meat and my BIFA nomination," she says. "The film is about a woman who is struggling to get up in the morning and struggling to be a mother." Even before playing Joyce Vincent, Ashton was interested in black women and mental health: she wrote a play, For All Those Women Who Thought They Were Mad, which was selected for the Royal Court's playwriting festival in 2009. "These are things that affect us all," she says. "Happy Toys has a black actress as the lead, the fabulous Jenny Jules, but it's not a 'banner' film. I'm just trying to make all the dots connect." She describes the film-making experience as "stressful but elating. I'm almost gleeful to be putting something out to the world."

We touch briefly on the recent Doctor Who casting and the Guardian poll that saw her edge out Chiwetel Ejiofor, Stephen Mangan and Ben Whishaw as our readers' favoured Tardis occupier. She thought it was a joke until she saw it online herself. "I never in a million years would've thought I'd end up on that poll," she says, still somewhat incredulous. "Me, as a mainstream character on the BBC, in a role previously filled by white men! What a wonderful way to illustrate how attitudes towards mainstream casting are beginning to change." She cackles. "It wasn't even that I wanted to be Doctor Who!"

It's time for her photoshoot. I accompany Ashton to the studio and, on the way, we see food critic Jay Rayner walking towards the front door. Ashton's eyes go wide. "Oh my God, it's Jay Rayner. Look!" Vod wouldn't even have noticed.

Series three of Fresh Meat starts Mon, 10pm, C4