The retailer said: 'When we last reported in November, the trading environment had become more difficult. Despite heightened levels of promotional activity over the Christmas period, including our two Christmas Spectaculars, significantly more stock was carried over into the end-of-season Sale compared with last year.'
The retailer said its markdown costs, as a result of the Sales, had increased by about£40 million.
M&S's food business traded disappointingly in October and November, but picked up over Christmas. Actual sales in food rose 1.7 per cent over the six week period, although like-for-like sales dipped by the same amount.
The board now expects profit before tax and exceptional items to be between£600 million and£625 million - at least£25 million below analysts' expectations.