The FTSE 100 dipped below the 5,000 mark this morning after a short-lived rally at the start of trading.
Heavy losses in the battered US markets have spread to the UK and sent the index of 100 leading shares down more than 3%.
UK shares rounded off a dismal week with further heavy losses despite better than expected jobs data in the US, as worries over the Eurozone crisis worsened.
Global markets are posting heavy losses as further weak economic data from the US deepens fears the country will fall into recession.
The Dow Jones is on course for its eighth consecutive day of losses following weak consumer spending figures.
Global markets climbed overnight on news the US has agreed a solution to its debt crisis, which will ease fears of the country losing its AAA-credit rating.
The Dow Jones closed more than 90 points lower on Tuesday amid escalating fears the US will default on its debt for the first time in its history.
News Corp's shares jumped 5.5% following yesterday's parliamentary hearing with the group's chiefs Rupert and James Murdoch.
Bank shares climbed in early trading, regaining some ground after Friday's stress test results caused sharp falls in the UK's major banks.
European indices have opened flat in early trading as markets pause for breath after posting losses of over 2% this week, hit by contagion fears across the Continent.