Britain's FTSE hits six-week low as mining shares slump

* Blue-chip FTSE 100 index down 0.5 pct

* Mining companies hardest hit on weaker metals

* Aberdeen, Babcock down as they trade ex-dividend

By Atul Prakash

LONDON, Dec 11 (Reuters) - Britain's top share index slipped to a six-week low on Thursday as mining shares fell on concern that metals demand is weakening and some stocks traded without the attraction of their latest dividend payouts.

Aberdeen Asset Management (Other OTC: ABDNF - news) , 3I Group, Associated British Foods (LSE: ABF.L - news) and Babcock were 1.2 to 3.1 percent lower as they went ex-dividend on Thursday.

The UK mining index declined the most among sectors, losing ground for a sixth straight session. Rio Tinto (Xetra: 855018 - news) , BHP Billiton (NYSE: BBL - news) , Randgold Resources and Anglo American (LSE: AAL.L - news) fell 2.3 to 4.6 percent.

"The FTSE 100 is being held down by its heavily-weighted mining sector as gold, silver and iron ore prices came down, reflecting the slowdown globally and within China," Jasper Lawler, analyst at CMC Markets, said.

"While the Chinese government continues to attempt its fine-tuning of the economy and holds off going whole-hog on stimulus, mining shares will be vulnerable."

Iron ore fell to its cheapest in more than five years because of a supply glut. Aluminium, nickel, gold and silver fell 0.2 to 0.8 percent. Copper was up 0.7 percent but has fallen nearly 5 percent in three weeks.

The mining companies put pressure on the FTSE 100 index , which was down 0.5 percent at 6,465.46 points by 1504 GMT. The index reached an intra-day low of 6,441.28 points, its lowest since late October.

"Worries about global growth, particularly the slowdown in China, will continue to put pressure on many commodities," John B. Smith, senior fund manager at Brown Shipley, said.

"FTSE 100 has fallen below 6,500. It looks slightly oversold and might try and rally, but downside pressures will remain into early next year."

Among mid-cap gainers, British telecoms testing company Spirent rose 6 percent after UBS (NYSEArca: FBGX - news) upgraded the stock to "buy" from "neutral." Energy services company John Wood Group rose 1.2 percent after it announced a $750 million, five-year contract from BP.

"Their message today is encouraging," Mark Ward, head of execution trading at Sanlam Securities, said, referring to John Wood Group. "I think they are still undervalued here." (Additional reporting by Alistair Smout; Editing by Jeremy Gaunt, Larry King)