Britain's FTSE hits three-week low as mining shares extend losses

* FTSE 100 down 1.2 percent

* Mining companies remain under 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 and Alistair Smout

LONDON, May 4 (Reuters) - Britain's FTSE 100 index slid to a three-week low on Wednesday as basic-resources stocks extended the previous day's losses and retailers came under pressure.

The FTSE 100 index dropped for a third straight session and closed down 73.57 points, or 1.2 percent, at 6,112.02 points, its lowest level since early April.

The UK mining index fell 4.2 percent after slumping 6.8 percent on Tuesday as copper prices slipped further on concern about weakness in global manufacturing activity.

Shares (Berlin: DI6.BE - news) in BHP Billiton (NYSE: BBL - news) fell 5.8 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.

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 3.2 percent. Anglo American, Antofagasta (Other OTC: ANFGF - news) and Rio Tinto (LSE: RIO.L - news) also fell.

Oil company Shell (LSE: RDSB.L - news) also ended lower, down 2.5 percent, trimming about 13 points off the FTSE 100. Shell said on Wednesday it was cutting its 2016 spending plans another 10 percent from the target set in February, when it bought BG Group. The company said it could cut further if it needed to .

London Stock Exchange (Other OTC: LDNXF - news) dropped 4.2 percent after ICE ruled out a counter-offer for the company, which is set to merge with Deutsche Boerse (LSE: 0H3T.L - news) .

Among retailers, Sainsbury's fell 6.3 percent after it reported a second straight year of profit decline and said it did not expect tough trading conditions to ease any time soon .

Tesco (Xetra: 852647 - news) was down 5.4 percent and Morrison fell 1.8 percent. A new Kantar survey showed the big four grocers were still being squeezed.

However, Next (Other OTC: NXGPF - news) rose 3.5 percent despite lowering sales guidance as investors took the advantage of its drop to a two-and-a-half-year low on Tuesday.

"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, Larry King)