Next shares opened four per cent lower as the retailer warned it could be forced to lower profit guidance if the "unusually warm" September weather continues.
In a trading statement posted this morning, the retailer said despite "several very strong weeks" during August's dip in temperatures, September's warmer weather "had the reverse effect". It now expects sales to rise six per cent during the third quarter, rather than the 10 per cent it had previously forecast, it said.
The retailer added past experience suggests those lost sales will be made up when the weather turns, meaning full-year profits are still expected to be "within our previous guidance". But it said if the warm weather continues, it could lower its full-year profit guidance range of £775m to £815m.
The retailer has shown impressive growth over recent months, reporting its "strongest sales growth for many years" in the first half of the year, with total sales up 10.3 per cent in the six months to the end of July, while pre-tax profits rose 19.3 per cent.
At the beginning of August, Next was valued at £5.3bn - bigger, for the first time, than rival Marks & Spencer, which is valued at £5.1bn.
Given Next's perceived strength, today's warning may also affect investors' confidence in rival retailers.