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* Q3 sales to date up 6 pct, below previous forecast
* May reduce profit guidance if warm weather continues
* M&S says no plans to change trading update schedule
* Shares fall up to 5.6 pct, rival retailers hit (Adds detail, trader and analyst comment, shares)
By James Davey
LONDON, Sept 30 (Reuters) - British retailer Next warned on Tuesday it will have to lower profit forecasts ifunusually warm autumn weather continues and shoppers don't buywinter clothing, denting shares across the sector.
Shares in Next, Britain's second biggest clothing retailerby sales, fell as much as 5.6 percent. Shares in Marks & Spencer, the country's largest clothing retailer, declined by upto 4.4 percent, while department store Debenhams weredown by up to 4.7 percent.
The comments had extra resonance coming from Next which hasoutperformed rivals for a decade due to a strong online offer,new store openings and diversification into new product areas,such as homewares, as well as new overseas markets. In July thecompany raised its guidance for annual sales and profit for thesecond time in three months.
"Next don't often lower guidance, so the fact that they havesaid they may do so due to the warmer weather is hitting theshares, which have had a strong run, and will also hit thesector if the weather remains unseasonal," said Securequitysales trader Jawaid Afsar.
September is on course to be the driest since records beganin 1910, according to Britain's Met Office.
Next's warning comes less than two weeks after theemployee-owned John Lewis, Britain's largest department storechain, became the first major UK retailer to say shoppers weredelaying purchases of winter coats, hats and boots because ofunseasonably warm and dry weather.
Swedish fashion retailer Hennes & Mauritz, theworld's second biggest fashion retailer, issued a similarstatement last week.
M&S said it had no plans to change its trading updateschedule. It is next due to update investors on how it is faringon Nov. 5.
"Next are probably being unnecessarily cautious, ahead ofinvestor meetings this week, but the market is unlikely to takeany chances and the shares will be unnerved," said independentretail analyst Nick Bubb.
OCTOBER'S IMPACT
Next, which trades from over 500 stores in Britain andIreland, about 200 stores overseas, and through its Directoryinternet and catalogue business, said third quarter sales todate were up 6 percent - lower than its previous forecast of up10 percent.
"Cooler weather in August resulted in several very strongweeks. However, warmer weather in the more important month ofSeptember has had the reverse effect," it said.
Next said that at present its profit forecast for the full2014-15 year remains within its previous guidance range of775-815 million pounds ($1.26-$1.32 billion), given on July 29and reiterated on Sept. 11.
"Our experience suggests that some lost sales are regainedwhen the weather turns. However, if this unusually warm weathercontinues for the full duration of October then we are likely tolower our full year profit guidance range," it said.
Cantor Fitzgerald analyst Freddie George said he wasmaintaining his "buy" stance on Next and 2014-15 pretax profitforecast of 805 million pounds.
"The mild weather...is impacting all retailers in the UK andis only a temporary phenomenon. The underlying trends, in ourview, remain positive," he said.
Shares in Next, up 36 percent over the last year, were down265 pence or 3.8 percent at 6,600 pence at 0905 GMT, valuing thebusiness at around 10 billion pounds. (1 US dollar = 0.6153 British pound) (Reporting by James Davey; additional reporting by SudipKar-Gupta,; editing by Keith Weir)
