The FTSE 100 Index ended a rollercoaster week in the red today as more oil price weakness and the latest political intervention by Labour party leader Ed Miliband hit energy stocks.

London's top-flight closed 20.5 points lower at 6740.6, or 2.5% off its level when trading ended last Friday.

It marked the end of a volatile few days which saw the FTSE 100 Index suffer its steepest one-day fall in five months on Tuesday before a couple of sessions of gains.

British Gas owner Centrica and rival SSE were lower after Mr Miliband's pledge to force a cut in household bills.

He wants Ofgem to have the power to order energy companies to cut tariffs by the end of the year if Labour gains office at the general election. Centrica fell 3.5p to 237.9p and SSE by 29p to 1462p.

Meanwhile the price of a barrel of Brent crude dipped close to 55 US dollars during the session, continuing its declines after its slump in recent months had seemed to steady when it topped 60 US dollars in February.

The latest slide left exploration firm Tullow Oil off by 3%, or 9.9p, at 298.3p, and rival BG Group down 26p at 812.6p. Heavyweights Royal Dutch Shell and BP were also down, with Shell off 47.5p at 2005.5p and BP 7.6p lower at 418.2p.

In New York, the Dow Jones Industrial Average was sharply lower due to worries about higher interest rates and the strength of the US dollar weighing on America's big exporters.

The same factor is better for Europe's manufacturers, as the single currency falls amid the major economic stimulus package feeding into the eurozone.

Germany's Dax and France's Cac 40 were ahead as the euro fell closer to parity against the greenback.

The pound, which is at near seven-year highs against the single currency, gained slightly at a little over 1.40.

But sterling plunged two cents against the US dollar to reach lows not seen since June 2010. It was at just over 1.47 at the close.

The pound's weakness came after official figures showed a worse than expected start to the year for the UK's construction industry as output slumped 2.6% in January.

In stocks, Premier Inn owner Whitbread was 75p stronger at 5335p after it was raised to buy by brokers at Deutsche Bank. They also set a new target price of 6000p on the stock, which is now trading near to a record high.

In the FTSE 250 Index, shares in JD Wetherspoon were 4% lower after half-year underlying profits dropped 1% to £37.5 million due to supermarket competition and a hike in pay and bonuses for pub staff. Shares fell 31.5p to 780p.

The biggest risers on the FTSE 100 Index were Meggitt up 15.5p at 575p, British Land Company up 19.5p at 824.5p, Reckitt Benckiser up 130p at 5840p and ARM Holdings up 24p at 1186p.

The biggest fallers on the FTSE 100 Index were Tullow Oil down 9.9p to 298.3p, BHP Billiton down 46p to 1389.5p, BG Group down 26p to 812.6p and Glencore down 8.4p to 277.4p.