(Close): Shares continued to tumble in London as worries over global growth prospects continued to preoccupy investors.
The benchmark FTSE 100 index plunged to new 12-month lows, dropping 92 points, or 1.4%, to 6,339.97.
Weak data from Germany this week has raised fears that the eurozone is heading for recession.
Travel shares have also continued to come under pressure on concerns over the impact of the Ebola virus.
The biggest faller in the FTSE 100 was Tullow Oil, which tumbled more than 7%, while the stockbroker Hargreaves Lansdown fell more than 6%.
"Negative sentiment is rife in the market right now, and indeed if you look around the globe there is no shortage of troubles to worry about," said Laith Khalaf, senior analyst at Hargreaves Lansdown.
"The eurozone is flirting with deflation, and while recovery in the US is gathering pace, the Fed is turning off the QE taps, for now at least.
"At the same time there are political tensions in the Middle East, Ukraine, and the spreading Ebola virus to concern investors."
Oil prices dropped sharply, with Brent crude hitting its lowest level for nearly four years, after Saudi Arabia said it increased production last month.
Demand for oil remains subdued because of weak economic growth in many parts of the world, while oil supplies have been increasing.
Brent crude for November delivery hit $88.11 a barrel at one point, its lowest level since December 2010. US crude was $1.30 lower at $84.47 a barrel.
On the currency markets, the pound was down 0.49% against the dollar at $1.60380, and fell 0.03% against the euro to €1.2696.
