By Sara Sjolin, MarketWatch

LONDON (MarketWatch)--The U.K.'s FTSE 100 index closed at its weakest level in almost seven weeks Thursday, with shares of Next PLC among biggest decliners after a disappointing earnings report.

The FTSE 100 index lost 0.5% to end at 6,799.62, marking the lowest closing level since late August.

The losses in London reflected an overall weakness in Europe and the U.S., where details of fresh sanctions on Russia and worse-than-expected U.S. weekly jobless claims bruised the investing mood.

Scottish referendum: The FTSE started out in positive territory on Thursday after a poll showed a lead for the camp against Scottish independence, calming fears of a breakup of the union. According to a poll for the Daily Record, 53% of the voters prefer Scotland to remain in the U.K., giving the pro-union camp a six-point lead over the "yes" campaign.

Over the weekend, a YouGov poll had indicated a majority of voters would support a separation. The uncertainty on the future of the U.K. sent the pound and stocks sharply lower on Monday, but sterling rebounded (GBPUSD) to $1.6224 on Thursday, from $1.6202 Wednesday afternoon in New York.

Movers: Shares of Next posted one of the biggest losses in the FTSE, down 3% after the fashion retailer posted earnings that were a bit worse than expected.

Shares of Royal Bank of Scotland Group PLC (RBS) added 1.1% after the bank said it would relocate its holding company to England in case of a "yes" vote for an independent Scotland.

Lloyds Banking Group PLC (LYG) also said it would move to England if the union is broken, sending the shares 1.2% higher.

Shares of Wm Morrison Supermarkets PLC inched 0.7% higher after the food retailer reported a drop in first-half profit, but raised its dividend and confirmed its full-year guidance.

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