Tough trading conditions sent shares in Debenhams tumbling 12 per cent after the store chain's margins suffered.

Like-for-like sales across the group in the 20 weeks to July 20 were above most analyst forecasts at 6.2 per cent.

But the gross margin was down 0.6 per cent because of additional promotional activity on summer merchandise as the retailer struggled with the unseasonal weather.

The summer sale got off to a slow start from July 8, hitting one of Debenhams' key trading periods.

Chief executive Belinda Earl said: "We are actively managing the business to support sales while controlling both costs and stock levels.

"However, our expectations for the second half of the financial year reflect the reduced gross margin currently being achieved."

The warning prompted a cut in forecasts. Seymour Pierce is now predicting final pre-tax profits of £154.5 million instead of £160 million and the shares tumbled.

Despite the disappointing trading update, Ms Earl was upbeat about the group's long-term future.

She said: "We remain confident in our strategy and are continuing to get strong returns from our investments.

"We have a number of significant developments planned for the next financial year, including five new stores openings and participation in a major new loyalty scheme."

Debenhams has stores in Brighton, Crawley, Eastbourne and Worthing.

Accountancy firm Deloitte and Touche warned the UK consumer boom was about to hit the buffers.

The High Street has helped the UK economy escape the worst of the global slump with low interest rates discouraging saving and a strong property market and low unemployment boosting confidence.

But Deloitte and Touche forecast consumer spending growth would drop from 3.7 per cent a year to about 2.7 per cent in the medium-term.

It cited a number of reasons, including consumer finances suffering from high levels of debt.