Britain's FTSE falls as slump in copper clobbers miners

* Mining index (Jakarta: ^JKMING - news) dives 8 pct as metals prices plunge

* World Bank cut to global growth forecast hits markets

* Premier Oil (LSE: PMO.L - news) down as expects $300 mln impairment charge

By Atul Prakash

LONDON, Jan 14 (Reuters) - Britain's top share index fell nearly 2 percent on Wednesday, with a plunge in metals prices on global growth concerns prompting jittery investors to exit mining stocks.

The UK mining index dropped 8 percent, the biggest one-day percentage fall in three years, after copper plunged more than 8 percent at one point to its lowest in 5 1/2 years, triggered by a wave of stop-loss selling following a downward revision to global growth by the World Bank.

The bank late on Tuesday lowered its global growth forecast for 2015 and next year due to disappointing economic prospects in the euro zone, Japan and some major emerging economies, which offset the benefit of lower oil prices.

"It's a straight read-across. Global growth estimates are being revised down and metals prices are slumping, forcing large investors to cut their exposure to the sector," David Battersby, investment manager at Redmayne-Bentley, said.

"Mining shares are expected to remain depressed in the near term as sentiment is very bearish."

Commodity majors Rio Tinto (Xetra: 855018 - news) , Anglo American (LSE: AAL.L - news) , BHP Billiton (NYSE: BBL - news) and Antofagasta (Other OTC: ANFGF - news) were down 5.7 to 10 percent. Glencore (Xetra: A1JAGV - news) slumped 11.5 percent, also hit by Citigroup (NYSE: C - news) cutting its target price for the stock.

Miners dragged down the blue-chip FTSE 100 index, which was 1.8 percent lower at 6,423.88 points by 1221 GMT after touching a one-week low of 6,418.75 at one point.

The FTSE 100 hit a peak of 6,904.86 points at the start of September, its highest since early 2000, but it then slumped to 15-month lows in October as weak European economic data knocked back stock markets.

Among other sharp movers, oil producer Premier Oil fell 3.7 percent after saying it expected to book a $300 million impairment charge due to the plunge in oil prices and planned to cut jobs and investment to rein in costs.

Oil companies across the globe are scrambling to deal with a 60 percent drop in crude prices in seven months, putting them under pressure to find cost savings.

Mid-cap video games retailer Game Digital (LSE: GMD.L - news) slumped 34 percent as heavy competition over holiday periods led to reduced pricing and bundling of games with consoles, hitting its margins. (Additional reporting by Sudip Kar-Gupta; Editing by Susan Fenton)