LONDON (AFP) - British high street mainstay Marks & Spencer on Wednesday announced an unexpectedly deep slump in clothing sales over the Christmas period.

The retailer suffered a 3.8 per cent fall in sales of non-food items in the 13 weeks up until Dec 29, leading to a worse-than-expected 1.8 per cent fall in overall like-for-like sales.

Chief executive Marc Bolland admitted in a statement that the non-food sales results were "not yet satisfactory".

He added that measures being taken by the new management team "will address" the weak figures.

"Our plan is to transform Marks & Spencer from a traditional UK retailer to an international multichannel retailer. We are making good progress against this plan," he explained.