Marks & Spencer Group shares fell sharply in London trading after the iconic British retailer posted disappointing holiday sales figures.

Britain's top clothing retailer reported a sixth consecutive slump in quarterly sales late Wednesday evening, with total sales for the 13 weeks ending on 29 December rose 0.3 percent, according to a company statement. Like-for-like sales, which measure trade from stores opened for at least a year, fell 1.8 percent overall and a steep 3.8 percent in the group's general merchandise unit. Food sales grew 0.3 percent, the company reported, less than analysts had anticipated.

The trading update was due to be published Thursday morning but was rushed out late Wednesday after details had apparently been leaked to Sky News.

M&S shares fell 4.2 percent, the steepest single-day decline in at least two years, to change hands at 355.3 pence, triming the 52-week gain to around 14 percent.

"Our Food business has performed very well with record sales over the key Christmas trading period," said CEO Marc Bolland. "Our General Merchandise performance is not yet satisfactory but we are confident that the steps being taken by the new management team will address this."

Food sales, however, continued to support the group's top line, with more than £330m - a company record - sold over the Christmas fortnight.

"Our strategy to focus on innovation worked, with over 700 new products launched during the quarter giving customers all the ingredients for a special M&S Christmas," the company said.

The company maintained its margin forecast of between zero and 25 basis points and predicted slower cost growth to offset slumping sales.

M&S rival Debenhams earlier this week posted record December sales as better promotions and a surge in online shopping lifted turnover at Britain's second-largest department store chain.

Sales for the 18 weeks ending on 5 January rose 2.9 percent, the company said in a statement published Tuesday on its website. December sales, which the company records during the five weeks prior to 5 January, rose 5 percent to a company record. Online trading, the group said, surged 39 percent over the full 18-week period.

"We expect the pressure on consumers' disposable incomes to continue in 2013," M&S said in the statement. "As a result we remain cautious about the outlook for the year ahead." The group will deliver fourth quarter sales data on 11 April.