Britain's FTSE retreats on weak Chinese, euro zone data

* FTSE 100 index falls 0.5 percent

* Weak Chinese, euro zone data hit miners, banks

* Centrica (LSE: CNA.L - news) hit after profit warning

* Johnson Matthey (LSE: JMAT.L - news) , Babcock gain after results

* ITV (LSE: ITV.L - news) falls as prospect of Liberty Global (NasdaqGS: LBTYA - news) bid fades

By Atul Prakash and Francesco Canepa

LONDON, Nov 20 (Reuters) - Britain's top share index fell for a second day on Thursday, hit by weak economic data from the euro zone and China and a profit warning from energy supplier Centrica.

The blue-chip FTSE 100 index was down 0.5 percent to 6,666.66 points by 1530 GMT, extending its retreat from an eight-week high hit on the previous day.

The industrial metals and mining indexes dropped 2.5 percent and 2 percent, respectively, after a private survey showed growth in China's immense factory sector stalled in November. China is the world's biggest metals consumer.

"It's not surprising that the market is reacting to weak commodity prices and disappointing Chinese data," said Henk Potts, director of global research at Barclays (LSE: BARC.L - news) .

"China has been the key influence in commodity markets over the course of the past 15 to 20 years, but the country is slowly going through a transition, moving away from being a manufacturing powerhouse. Its influence on commodity markets is likely to diminish."

Global miners Rio Tinto (Xetra: 855018 - news) , Anglo American (LSE: AAL.L - news) and BHP Billiton (NYSE: BBL - news) each fell more than 2 percent.

Banks, whose profits tend to depend on economic growth, also came under pressure as a survey showed business growth in the euro zone has been weaker than any forecaster expected this month. New orders have meanwhile fallen for the first time in more than a year despite further price-cutting.

Among other single stocks, Centrica, Britain's largest energy supplier, fell 1.6 percent in brisk volume after it cut its full-year earnings outlook on the back of a steep drop in energy demand due to mild weather and the extended outage of two nuclear power plants.

On the upside, the world's largest autocatalyst maker Johnson Matthey rose 5.7 percent after posting a small increase in half-year profits thanks to strong autocatalysts sales, and lifting its profit forecast for the year.

British engineering and support services firm Babcock rose 5.8 percent after reaffirming its full-year profit outlook and raising its dividend after posting a 32 percent rise in underlying first-half pretax profit.

Broadcaster ITV fell 1.5 percent in late trade after Europe's leading cable operator Liberty Global said it had no plans to bid for the British firm. (Editing by Hugh Lawson)