Debenhams has lost ground to its department store rivals

Like-for-like UK sales - which exclude the impact of new stores - fell 4% in the 19 weeks to 13 January, following lower-than-expected clothes sales.

Including new store space, total sales rose 6.3% in the period, but Debenhams said the market remained tough.

In December, the firm had warned that sales were being hit by mild weather.

'Challenging' market

Debenhams said that disappointing clothes sales and the impact of integrating the Roche stores in Ireland, which it bought last year, would hit half-year profitability.

Chief executive Rob Templeman said the firm's "sales performance has improved since we reported figures for the period to 10 December 2006 but the market remains challenging".

He added that "we are cautious about the outturn for the rest of this financial year".

While Debenhams struggled over Christmas, rival department store groups have enjoyed a better time.

John Lewis saw like-for-like sales at its stores leap 10.8% in the five weeks to 6 January, while same-store sales at House of Fraser were up 7.3% in the four weeks to 30 December.