Britain's FTSE hits 3-week low as miners extend losses

* Blue (OTC BB: BUES - news) -chip FTSE 100 down 1.2 percent

* Miners come under further pressure

* Sainsbury (Amsterdam: SJ6.AS - news) 's down on poor trading outlook (ADVISORY- Reuters plans to replace intra-day European and UK stock market reports with a Live Markets blog on Eikon - see cpurl://apps.cp./cms/?pageId=livemarkets for site in development. See the bottom of the report for more details)

By Atul Prakash

LONDON, May 4 (Reuters) - Britain's commodity-heavy FTSE 100 index slipped to a three-week low on Wednesday, with basic resources stocks extending the previous session's hefty losses and retailers under pressure.

The blue-chip FTSE 100 index dropped for a third straight session and was down 69.39 points, or 1.1 percent, at 6,116.20 points by 1348 GMT, dropping to its lowest level since early April.

The UK mining index fell 2.8 percent after slumping 6.8 percent on Tuesday as copper prices slipped further on lingering concerns about a weakness in global manufacturing activity.

Shares (Berlin: DI6.BE - news) in global diversified miner BHP Billiton (NYSE: BBL - news) , fell 4 percent, after federal prosecutors in Brazil filed a 155 billion-real ($43.5 billion) civil lawsuit against iron miner Samarco and its owners Vale and BHP over the fatal collapse of a dam in November.

"The overnight news of a fresh legal challenge suggests that the March settlement between BHP, its domestic partner Vale and the Brazilian government was just the beginning of the road," Mike van Dulken, head of research at Accendo Markets, said.

"A silver lining at this early stage is the shares holding above January rising support," he said, adding its share losses were limited by hopes that a smaller figure could ultimately be agreed.

Commodity miner and trader Glencore (Xetra: A1JAGV - news) , which reported a fall in output of copper, zinc, lead, coal and oil following a decision to cut production because of low prices, was down 3 percent, while Anglo American (LSE: AAL.L - news) , Antofagasta (Other OTC: ANFGF - news) and Rio Tinto (LSE: RIO.L - news) also fell.

Oil heavyweight Shell (LSE: RDSB.L - news) also fell, down 1.8 percent after results to trim 9 points off the FTSE 100.

The firm reduced its 2016 spending plans on Wednesday by another 10 percent from the target set in February when it completed the acquisition of BG Group (EUREX: 1007667.EX - news) , and said it could cut further if needed.

London Stock Exchange (Other OTC: LDNXF - news) slumped 6.7 percent after ICE ruled out a counter offer for the firm, which is set to merge with Deutsche Boerse (LSE: 0H3T.L - news) .

Retailers were broadly under pressure, with supermarket Sainsbury's falling 7.1 percent after saying it did not expect tough trading conditions to lift any time soon as it reported a second straight year of profit decline.

Tesco (Xetra: 852647 - news) was down 3.9 percent and Marks & Spencer (Other OTC: MAKSF - news) fell 1.8 percent, the sector also hit by a new Kantar survey, which showed the big four grocers were still being squeezed.

However, Next (Other OTC: NXGH - news) rose 5.9 percent despite lowering sales guidance as investors took the advantage of its drop to 2-1/2-year low in the previous session.

"We expect some pent up demand to come through from May, as temperatures rise. As such we expect some short term relief for Next's trading," analysts at RBC Europe said in a note.

"Also sterling has recovered some lost ground versus the US dollar, meaning there will be less upwards pressure on pricing from next year."

ADVISORY- Reuters plans to replace intra-day European and UK stock market reports with a Live Markets blog on Eikon (see cpurl://apps.cp./cms/?pageId=livemarkets for site in development). In a real-time, multimedia format from 0600 London time through the 1630 closing bell, it will include the best of our market reporting, Stocks Buzz service, Eikon graphics, Reuters pictures, eye-catching research and market zeitgeist. Breaking news and dramatic market moves will continue to be alerted to all clients and we will continue to provide a short opening story and comprehensive closing reports.

If you have any thoughts, suggestions or feedback on this, please email mike.dolan@thomsonreuters.com.

Mike Dolan, Markets Editor EMEA. (Reporting by Atul Prakash; Editing by Janet Lawrence)