Next chief executive Simon Wolfson has voiced fears that the growing swine flu epidemic could threaten second-half trading.

He said the size of its impact remains unknown but warned: “If large numbers become incapacitated it could have a real downside effect.”

Next brought forward its trading update this week after good weather helped it perform ahead of expectations. Total sales grew 1.4 per cent in the 25 weeks to July 18 and like-for-like sales were down 1.9 per cent.

Wolfson said that although Next had a good season the main reason for recent strong performance, particularly in fashion, was the weather. He added: “The ranges have been better and we have done well with some of our sourcing negotiations.”

In light of the strong performance Next has raised its internal profit forecast by £30m – a hike of £15m for each half-year.

Next said that without a weather impact in the second half it expects like-for-like sales to be down between 3.5 and 6.5 per cent. It does on anticipate any collapse in consumer sentiment in the second half and expects the consumer environment to be similar to the first half.