Last year, Isabel Greenberg, the winner of the Observer/Jonathan Cape/Comica graphic short story competition, bagged the prize on her third time of trying. But Corban Wilkin has gone one better than that, having won the 2012 prize – the sixth in its history – on his fourth go. How does it feel to have pulled it off after so long? Pretty good: after all, he beat 200 other cartoonists along the way. "The only thing I'm sad about is that I won't be able to enter again. I've loved doing it over the past few years. The brief is tricky – a very limited format and yet complete freedom of subject matter – but it's a challenge I relished. Once you enter, your writing improves pretty quickly. Four pages is a small space in which to tell a proper story."

Wilkin, 22, who is originally from Colchester, studied illustration at Middlesex University; his influences include the great Canadian cartoonists Craig Thompson ("his drawings are spot on") and Seth. His winning entry, "But I Can't", is a story of friendship, obsession and alien landings. The judges (Hannah Berry, author of the graphic novel Britten and Brülightly; Paul Gravett, director of Comica; Dan Franklin, publisher of Jonathan Cape; Suzanne Dean, Random House's creative director, and yours truly) liked Wilkin's use of colour; he uses Indian ink and watercolour, which he applies with a brush. But we were also impressed by the way he takes his characters, Lucy and Harriet, from childhood through to adulthood in just four scant pages. Where did this eerie story come from? "When I was about seven, I had a friend who lived nearby and we were both into UFO sightings," says Wilkin. "We went through a brief but memorable phase of sending signals in to space with a walkie-talkie. Years later, I tried to imagine what it would be like if someone somewhere was to cling on to that childhood interest, only for it tear them from their increasingly sceptical friends."

Wilkin knew he wanted to draw comics from the age of 16, when he read the rather fantastic Understanding Comics: The Invisible Art by Scott McCloud. "Until that point, I always thought I'd illustrate novels. But then I became crazy about comics and have been ever since." What will he do next? "Finish my graphic novel, which should take about a month. It's called Breaker's End and it's about a couple who live in a tent in the woods. Hopefully, winning this is going to help me to find a publisher for it. After that, I'll start another one. Repeat until death." The prize money (£1,000) is, he says, extremely welcome. "To be honest, this has come at the right time. I'm broke. Unfortunately, it may have to go on rent. But I'll stock up on art materials, too. My brushes are expensive."

Though the standard for entries was perhaps a little lower than in previous years, it was still tricky to choose a runner-up. In the end, we went for "I, Yeti" by Steve Tillotson, a gorgeous tale of loneliness and ice, starring a very large, very hairy yeti. Tillotson never intended to be a writer of comics; having done an MA in print-making at the Royal College of Art, he always thought he would be what he calls a "proper" artist. Gradually, though, his work became ever more driven by narrative and in 2005 he started writing his Banal Pig comics. His influences include Daniel Clowes and Chris Ware, but also the comics that he grew up with: the Beano, the Dandy, Buster and Whizzer and Chips.

Like Wilkin, he has entered the competition before. "Twice. My plan was to keep entering every year until I won. [But even being runner-up] is surprisingly vindicating. A lot of cartoonists are extremely self-critical and I'm no exception; it's quite a lonely business. This is a big morale boost and it's nice to see how much I've improved since the first time I entered in 2009."

He designed his story so he could play around with scale in his pictures: "I really like drawing mountains for some reason… my yeti character has been in my sketchbook for a while." What's his plan for the future? "I've got a few ideas for graphic novels bubbling away that I'm really excited about, and I'm involved in organising the Leeds Alternative Comics Fair. Comics events are a bit under-represented in the north."

■ A selection of prize winners, past and present, can be seen at an exhibition at Foyles from 4 November until 16 November (Foyles, 113-119 Charing Cross Road, London, WC2). Comica, the London International Comics festival, starring Posy Simmonds, Bryan Talbot, Alison Bechdel and many others, runs until 30 November at venues across London. For more details, go to comicafestival.com