Jane Shepherdson, the celebrated former brand director of Topshop, is to become chief executive of the high street womenswear chain Whistles, it was announced yesterday.

The label has been acquired from its current owners, Mosaic, by a newly formed company in which Shepherdson and her team have part ownership. The Baugur Group, an international investment company, is the lead shareholder and Glitnir bank is also an investor.

Ms Shepherdson said Baugur approached her soon after she left Topshop but, after discussing numerous different proposals with them and other companies, this was the option she felt the most comfortable with. She added, "This is a very exciting venture and I am thrilled to be taking over such an established British brand with enormous potential."

Once described as the most powerful woman in British fashion by the industry magazine Drapers, and the recipient of an MBE for services to retail, Ms Shepherdson is widely credited with reinvigorating Topshop's fortunes after she became its brand director in 1999. In 1998, Topshop made a £9m profit; by 2006 she had increased it to £110m. Not only that, it had become a fashion mecca – the shining jewel in the slightly rusty crown of Philip Green's Arcadia empire. It was newly fashionable for mothers and daughters, trust-funders and students alike to shop at Topshop, and its clothes regularly appeared in the pages of Vogue.

Ms Shepherdson attributes her success there to learning to "trust my own instincts and be very aware of people's boredom with fashion cycles". That wasn't all she acquired from the brand, however - the marketing director and finance director on the new Whistles management team are both former Topshop colleagues.

Her departure from Topshop in October 2006 coincided with the recruitment by Philip Green of the supermodel Kate Moss to design a clothing range. It led to widespread speculation that she was upset at being insufficiently consulted about the move. Arcadia swiftly issued a statement saying Ms Shepherdson had just decided it was, "time for a change" and yesterday she declared: "I decided to leave Topshop because it was the right time. It had absolutely nothing to do with Kate Moss."

After leaving Topshop, Ms Shepherdson took advisory roles for the ethical brand People Tree and the charity Oxfam. She said it was a priority to bring some of her ethical knowledge to Whistles.

Her willingness to embrace consumers' increasing interest in ethical brands and ways of shopping has cemented her reputation as more than just a talented executive with the Midas touch.

She is seen as a barometer for the fickle habits of today's consumers, so her next move will be watched because it is likely to be interpreted as a clear signpost towards which way shoppers' tastes and, by extension, profits are headed.

She said: "I think fashion is in an interesting position at the moment. It has become very polarised. There is an awful lot at the discount end of the market and it has become cheaper and cheaper, while the designer end has become more and more expensive.

"There is a gap for people who want to buy beautiful quality clothes but can't afford designer prices."