The twisted sisters who finally got their act together

Sibling rivalry? You bet. That's what makes Toby a superb sketch duo

The Andrews, the Nolans, the Minogues. Down the decades there have always been singing sisters. Stand-up sisters? Not so much. The comedy double act is a tricky enough dynamic without throwing the tensions of a sisterly relationship into the pot. Nothing daunted, Sarah and Lizzie Daykin have embraced twenty-odd years of sibling rivalry and used it as the foundation for their dark-hearted duo, Toby.

Last summer, their show Lucky was a word-of-mouth hit at the Edinburgh Fringe. A refreshing change from the macho, all-boy gangs or girl bands in matching outfits who tend to rule the sketch circuit, here was a strange pair – one in a prom dress, the other in jeans and a stripy T-shirt – performing surreal, unsettling sketches while battling to keep a lid on family feuds.

Among their skits is an edgy dinner date which spirals into a series of puns ("Just have the steak, Diane") and a jazz-dance about puberty. More League of Gentlemen than Marx Brothers, the twist is the strained Beckettian dynamic which bubbles under every routine. Sarah, 27, is the older sister, a drama-school brat with stars in her eyes who dabbles in Kabbalah and already has a spell in The Priory on her CV. Lizzie is three years younger, quieter and less glamorous, a talented singer who has given up music school to perform with her sister but finds herself shooed to the shadows or manning the tech desk, the better to shine the spotlight on Sarah.

Their rivalry is heightened for the stage, but it has its roots in childhood. "As little kids we both loved performing," recalls Lizzie. "Sarah would put on plays at home where I would just be used as the little bird or something." Their first show had the tagline "Sisters perform inappropriate sketches in a bid to win their mother's attention", while Lucky, their second, features This is Your Life-style video interviews with their parents, in which they assess the relative talents of their daughters. "We were quite cliquey and ganged up on our Mum as kids," says Sarah. "We found a lot of humour in that. Mum likes to think she's our muse – she doesn't really get the joke."

The sisters are still inseparable. They live together in north London and work together part-time in a call centre in Dalston. Two years ago, they hit "crisis point": Sarah was a drama school grad, unable to get a foot in the door, while Lizzie had tried and failed to become a jazz singer. One day a friend offered them a 10-minute spot on a comedy mixed bill at the Camden Fringe, so they started writing together. "We didn't plan it," says Sarah. "We've always had the same sense of humour and agree on comedy we like."

In 2010 they took their first show up to the Free Fringe. Simon Pearce, the producer behind the Invisible Dot – comedy home to Tim Key, Daniel Kitson and Jonny Sweet, among others – saw it and picked them up for a run on the main Fringe last summer. Now they are reprising Lucky at London's Soho Theatre and are writing a television show, based on their lives and set in a call centre. Sarah recently appeared in the pilot of Chickens, the new wartime comedy from Inbetweeners Simon Bird and Joe Thomas, while Lizzie is writing sketches for BBC Comedy. Both have bit parts, "as geeky quiz team members", in Sharon Horgan's new prison sitcom, Life Story.

Why Toby and not The Daykin Sisters? "We were playing the game of what your name would be if you were a boy," says Lizzie. "Everybody said that mine would be Toby. It doesn't indicate that you're two girls, which helps when people are booking tickets. And it's fairly memorable."

"Plus our Mum hates it – so we knew that it was the right choice," adds Sarah.

Toby, Soho Theatre, London W1 (020 7478 0100; sohotheatre.com) Thursday to Saturday & 3 to 5 March