Shares slide ahead of U.S. data crunch LONDON (Reuters) - World shares fell for a third day on Wednesday and gold was at a five-month low, with focus back on the risks of the U.S. Federal Reserve starting to trim its bond-buying economic stimulus as soon as this or next month. The to-and-fro of when the Fed will begin to halt the flow of cheap dollars has dominated trading worldwide for months and a run of data ending in the main U.S. jobs indicator - non-farm payrolls - on Friday may yet tip the balance again. Polls of analysts and traders still point firmly to the U.S. central bank holding fire until next March but some stronger data has reheated speculation it could move earlier. That prompted investors to cash in gains from recent rallies, although European stocks .FTEU3 saw a steadier start after suffering their biggest tumble since August on Tuesday. Still, Johan Jooste, head of fund manager Julius Baer's London investment office said it wasn't necessarily the start of the Fed's withdrawal that would drive the market's reaction. The whole market has been focused on when tapering will start, but what I would ask (incoming Fed chief) Janet Yellen is when does she perceive it ending. If the Fed starts in Jan or March I'm not so sure that's necessarily the big deal, but it's a bigger deal if it ends it quickly. A sharp 2.2 percent fall for the Nikkei in Tokyo .N225 left MSCI's world share index down 0.3 percent on the day..MIWD00000PUS The dollar .DXY retreated against the yen and a basket of currencies in the FX market as traders used the uncertainty to lock in some of their recent profits on the greenback. Benchmark U.S. treasury yields edged back toward 2.8 percent in early European trading. Wall Street, however, was expected to see a small rebound after the Dow Jones industrial average .DJI the S&P 500 Index .SPX dropped on Tuesday. Ahead of the European Central Bank's meeting on Thursday, mixed euro zone PMI data reinforced the differing fortunes of its main economies, though having only cut rates last month additional measures from the bank look unlikely for now. One of Europe's best performing economies is currently the UK, but high-flying sterling saw its wings clipped as growth in Britain's service sector slowed a little last month, breaking a run of upside data surprises. The pound fell to session low of $1.6326 and 83.23 pence to the euro while UK government bonds pared their morning losses. The specter of tapering in the Fed's bond-buying is also spooking emerging market shares and currencies in particular. They were among the hardest-hit when Fed Chairman Ben Bernanke first floated the taper idea back in May. The Indonesian rupiah weakened 0.9 percent to 11,990 rupiah per dollar after earlier falling to 12,000 to match a near five-year lows touched last week. The Thai baht edged down 0.2 percent to 32.25 baht per dollar after protesters in Thailand trying to bring down the government rallied at national police headquarters. Their leader said the protesters' fight would go on despite efforts to defuse the crisis. The Australian dollar sank 0.8 percent to $0.9060 having earlier fallen to a three-month low of $0.9045, after Australia's July-September gross domestic product growth fell short of market expectations. Gold and silver, which like stocks have benefited from the U.S. stimulus because of inflation fears, traded near 5-month lows. Gold last stood at $1,221.26 per ounce while silver traded at $19.11, having slipped to $18.94 on Tuesday. Oil prices jumped ahead of this week's OPEC meeting, with U.S. crude futures hitting a five-week high. Reporting by Marc Jones