A trader monitors the screen on a trading floor in London.

London - Britain's top share index fell to six-week lows on Wednesday, on investor concern about the effect a further reduction of US monetary stimulus would have on emerging markets.

Investors have been on edge in the past days as unease about Chinese growth and the withdrawal of US monetary stimulus spread from emerging-market currencies to the world's big stock markets.

A huge rate hike by Turkey's central bank to defend its currency sparked a rally in global stocks earlier in the day. But both the lira and stock markets were back under pressure as investor attention switched to the conclusion of the Fed's two-day policy meeting later on Wednesday.

“I think the big concern that we saw ... last year, when they mentioned they were going to pull the plug on the bond-buying programme, that the people that would suffer would be the emerging markets - I think we're seeing a bit of a spillover on that,” Mark Priest, sales trader at ETX Capital, said.

“I think they're definitely going to start tapering ... There are rumours flying around (for another reduction of) $10 billion.”

The FTSE 100 was down 38.99 points, or 0.6 percent, at 6,533.34 points by 18:12 SA time, having swung in a wide range between 6,482-6,572 during the session.

The index had risen 0.3 percent on Tuesday after a sharp drop of around 4 percent the previous three sessions as emerging market currencies weakened.

The mining index limited losses, up 1.5 percent, helped by a 6.1 percent jump to the top of the FTSE 100 by Antofagasta.

The Chilean miner posted record full-year copper production and said its cash costs for this year would be in line with 2013.

Anglo American, meanwhile, notched a 5.7 percent rise after annoucning a better-than-expected rise in iron ore production in the fourth quarter.

Technical analysts were bearish on the FTSE 100.

“If we close well within the bottom half of today's range, then that would imply further downside, and we could see a squeeze towards thelows of December,” Barclays Capital analyst Lynnden Branigan, said. - Reuters