By Atul Prakash and Alistair Smout
LONDON (Reuters) - Britain's main share index slipped to its lowest level in nearly four months on Thursday due to growing nervousness about next week's vote on UK membership of the European Union.
Investors were also cautious after the Federal Reserve cut its growth forecast and Fed Chair Janet Yellen acknowledged Britain's possible EU exit would have consequences for economic and financial conditions globally.
"Usually traders will push equity markets higher if the Fed is going to stay on the dovish side, but today is not that day," Naeem Aslam, chief market analyst at TF Global Markets, said.
"Brexit anxiety has its own flavour and it is very bitter."
Opinion polls have shown unexpectedly strong support for Britain leaving the EU in the June 23 referendum, prompting concerns about the impact on the bloc, the unity of the United Kingdom and the wider impact on global financial markets.
Polls by Ipsos MORI and Survation on Thursday showed the "Out" campaign in the lead, confirming a recent trend that has shown the momentum is with those who wish to leave the EU.
The blue-chip FTSE 100 index (FTSE) was down 0.7 percent to 5,922.12 points by 1131 GMT after falling to 5,907.63, its lowest since late February.
Cyclical stocks were the worst hit, with the UK banking index (FTNMX8350) falling 1.4 percent to a two-month low. Shares in Royal Bank of Scotland (L:RBS), Barclays (L:BARC) and Lloyds (L:LLOY) fell between 1.7 and 2.6 percent.
"If there was a vote to leave the EU, the immediate reaction in banking stocks would be quite dire. We've had an atrocious performance in banks quite broadly so far this year, and if economic growth is set to be hit ... then you get out of banks," said Chris Beauchamp, market analyst at IG.
Mining stocks also came under pressure, with Anglo American (L:AAL) and BHP Billiton (L:BLT) down by 4.6 and 2.7 percent respectively.
However, gold producer Randgold Resources (L:RRS) rose 4.3 percent, the top gainer in the FTSE 100 index, to its highest in nearly two years on wider economic uncertainty.
Among other movers, 3I Group (L:III), Mediclinic International (L:MDCM) and Severn Trent (L:SVT) fell 2.6 to 4.5 percent after their shares traded ex-dividend.
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