* FTSE down 0.6 percent, FED statement cautious
* Banks slide as Moody's reviews Spain rating
* Commods fall as investors switch to dollar
By David Brett
LONDON, Dec 15 (Reuters) - Banks led Britain's top shares lower on Wednesday, after cautious announcement from the U.S. Federal Reserve overnight, and a potential downgrade to Spain's sovereign credit rating weighed on sentiment.
By 0903 GMT, the FTSE 100 index was down 32.29 points, or 0.6 percent, at 5,858.92 as investors took a flight from risk, and having ended up 5,891.21, a closing level not seen since June 2008.
Banks were the biggest fallers on London's blue chip index, led by Barclays down 3.1 percent, as doubts over the global economic recovery reared its ugly head.
Moody's Investors Service said it put Spain on review for a possible downgrade because of its high funding needs and doubts about its banking sector and regional finances, which put more pressure on the euro.
Moody's announcement followed S&P's threat on Tuesday of a downgrade for Belgium.
Overnight in the U.S., the Fed, in a policy statement said the economic recovery was still too slow to bring down unemployment, and reaffirmed its commitment to buy $600 million in government bonds.
"Euro zone worries coming back into focus and the cautious note struck by the Fed are driving the market lower," Martin Dobson, head of trading at Westhouse Securities, said.
"I think we are still a long way from getting a resolution on the euro zone and these problems will stay with the market over the next year or so."
Mining and energy shares fell along with commodity prices as risk appetite ebbed, and metal prices fell against the backdrop of a strengthening dollar.
BA STRIKES
British Airways was 2.5 percent cheaper after the trade union representing cabin crew at the airline said it would ballot members next week over fresh strike action in a dispute that has so far cost the airline 150 million pounds ($238.1 million).
On the second line, SuperGroup slumped more than 16 percent after the firm behind the Superdry fashion brand reported results, with Peel Hunt putting its rating under review citing valuation grounds, and with margins likely to come under pressure from rising commodity prices.
United Utilities, the only FTSE 100 company to go ex-dividend on Wednesday, fell 2.4 percent.
On the upside, Capital Shopping Centres rose 2.7 percent as Simon Property Group Inc, in a struggle for control over the firm, proposed a 425 pence per share offer valuing the British mall owner at about 3 billion pounds.
Peer, Anglo-French property investor Hammerson added 0.6 percent after offloading the Bishops Square office site in the London's finance district in a deal worth nearly $900 million to J.P. Morgan Asset Management.
Pearson gained 0.6 percent as Deutsche Bank upgraded the publisher to "buy", saying that a growing cash pile and heavy investment in technology puts it in a strong position. Investors will watch the CBI distributive trades data for December released at 1100 GMT for more clues on the state of the British economy. ($1=.6301 Pound) (Editing by Sharon Lindores0