Womenswear retailer Bonmarche has lost almost one third of its stock market value after it warned over profits and said its boss was leaving the business.

The chain said due to "very challenging" conditions its full-year profit would come in at between £10.5 million and £12 million, compared with previous expectations of £13.4 million. This comes just three weeks after the firm said its annual forecasts would be unchanged.

The business, which employs just over 3,100 staff across 292 shops and concessions, added that its respected chief executive Beth Butterwick will leave the firm to head up rival retailer Karen Millen once a replacement is found. Shares plunged 29 per cent.

The Wakefield-headquartered firm said: "Trading conditions during December, particularly since Black Friday on November 27, have been very challenging, and have not normalised.

"The board's view is that these trading conditions are likely to continue for the remainder of the winter season and it has therefore revised its profit expectations for the current financial year."

Analysts at Investec said: "A disappointing update from Bonmarche, coming just three weeks after its first-half results."

They added shares in the group were likely to remain under pressure until a new chief executive is announced.

Bonmarche chairman John Coleman thanked Ms Butterwick for her "exceptional contribution" in leading the firm through a busy four years.

Mr Coleman added: "She has led the business through a transformative period, through the acquisition by an affiliate of Sun Capital Partners in 2012, the initial public offering on the Alternative Investment Market in 2013, and most recently the company's transition to the London Stock Exchange's main market as one of the UK's largest women's value retailers."

Ms Butterwick's new retailer Karen Millen has shops in over 65 countries across six continents including flagship stores in London's Knightsbridge and New York's Fifth Avenue.