LONDON — A clutch of Britain’s top retailers and e-tailers are set to unveil Atterley.com, a fashion Web site that aims to fill a market niche and appeal to young professionals who’ve outgrown fast fashion on the high street.

The site, which will go live on Monday, is backed by a consortium of investors including former Tesco chief executive officer Sir Terry Leahy; The William Currie Group, an early investor in Asos.com, and Artemis Fund Managers.

Atterley.com is run by Asos veterans Sally-Anne Newson, whose title is ceo, and Jon Kamaluddin, executive chairman and one of the investors. Becky Leeson, Atterley’s creative director, has worked for Topshop and Asos.

Kamaluddin, previously chief financial officer and international director of Asos, has said he plans to take the Atterley business to revenues of 100 million pounds, or $154 million, by 2020. The company did not disclose its current sales, although Newson admitted during an interview here they were “small.”

Price points are similar to those of Swedish high street brand Cos, with a cotton denim shirtdress costing 48 pounds, or $74, and occasion dresses commanding up to 75 pounds, or $115. The focus is on chic wardrobe building blocks for work and weekend.

“The site is for style-conscious women who’ve graduated from high street fast fashion,” said Newson, who was most recently business development director for Asos. “She wants newness in her wardrobe, and something that feels aspirational with great fit and style.”

Newson said she hopes Atterley can occupy the “white space” between retailers such as Topshop and Zara on one end, and Sandro and Whistles on the other. “Cos is the only brand that’s currently playing that space,” she said.

Leeson said she has been leveraging her sourcing and factory contacts built up through nearly two decades on the high street to deliver quality clothing to time-poor women.

She is sourcing in the U.K., Europe and India and her fall 2015 lineup includes a gray wool suit with belted jacket and cropped trousers; a lace-trimmed white shirt; a print dress with a drawstring waist and high collar; a black leather shift dress with a judo-inspired belt, and coats made from shearling or a cashmere blend.

“I want the customer to open the wardrobe of Atterley clothing and know the pieces will work together. We’re offering really nice fabrics and silhouettes that are always wearable and not difficult,” she said.

Atterley was founded as Atterley Road in 2011 by Katie Starmer-Smith, who’d worked as a designer for the British brand Jigsaw, and Edward David, whose background was in financial services. It originally offered a collection of contemporary, accessible Scandinavian labels such as Day Birger Et Mikkelsen, and generated more than 2 million pounds, or $3.1 million, in sales in the first 12 months. But building a site on the back of a variety of brands, many of them little-known, proved to be a challenge, and last year, the company secured 2 million pounds in funding from the consortium.

The founders are now minority shareholders, with the new investors holding a majority stake.

“It’s very hard to build loyalty with other people’s brands,” said Newson of the decision to focus on the in-house label. She said the new name Atterley reflects the focus on one collection rather than a “street of brands.” The site will continue to carry specialist names such as Seafolly swimwear.

The aim is for the site to consist of 80 to 90 percent own-brand products. Leeson said once clothing is up and running, the plan is to build up footwear and bags.

Content is fully shoppable, and the site aims to show the customer various ways to wear one item, style what she’s already put in her basket, and demonstrate how the clothes can fit a variety of lifestyles. “Today, customers want you to be more than a shop,” Newson said.

She added that the new management has tried to remain faithful to Starmer-Smith’s vision of providing an aspirational wardrobe to women over 30. “The vision hasn’t changed, but how we deliver that vision has,” she said.