Update: The FTSE 100 has tumbled below the 6,000 mark as a fresh slump in the price of oil hurt the index, while stocks with links to South Africa were hit by the tumbling rand.
The UK blue-chip index fell 113 points, or 1.9%, to 5,974, with Old Mutual (OML) rooted to the bottom of the index, down 10.8% at 155.6p, as the insurer's South African business was hit by fresh falls in the rand following the sacking of the country's finance minister.
Energy stocks were also hit hard by a slump in the oil price to £38.60 a barrel, down 2.8% on the day at a seven-year low, after the International Energy Agency warned of oversupply until at least the end of next year.
Miners fell heavily, with Anglo American (AAL) worst hit, down 7.3% at 295.5p after analysts at Goldman Sachs cut their target price on the stock.
'It's the first time the UK index has been below 6,000 since the end of September and marks the end of one of the worst weeks for the commodity-laden index in an already trouble-filled 2015,' said Connor Campbell, financial analyst at Spreadex.
'What is worrying is that this weekend brings with it the latest Chinese industrial production data, the kind of figure that, if it underperforms expectations, may only help escalate this current commodity collapse.'
FTSE hit by South African political turmoil
The slump in the rand sparked by the sacking of South Africa's finance minister has taken a chunk out of the share prices of FTSE 100 companies with significant exposure to the country.
Insurer Old Mutual (OML), which is listed in both London and Johannesburg, fell 8.8% to 158.9p, in its second day of heavy falls. The shares are now down 18.5% over the last two days. Mondi (MNDI), the packaging and paper company with a South African division, fell 2% to £12.90.
That weighed on the FTSE 100, which dropped 26 points, or 0.4%, to 6,062.
The fall-out extended outside the top 100 with South African bank and asset management group Investec (INVP) dropping 8.1% to 431.9p.
South African platinum miner Lonmin (LMI) was meanwhile the heaviest faller on the FTSE Small Cap index, down 6.8% at 0.96p.
The rand hit an all-time low after South Africa's president Jacob Zuma sacked finance minister Nhlanhla Nene (pictured), who has been attempting to rein in government spending as the country's economy struggles to grow.
'Removing him after just two-and-a-half years and installing the unknown David van Rooyen is a decision that has sent the rand to all-time lows and resulted in foreign investors running for the savannah, worried about the impact on an already troubled yet key mining sector,' said Mike van Dulken head of research at Accendo Markets.
On the FTSE 250, International Personal Finance (IPF) tumbled 22.5% to 250p as the lender warned that new legislation in Slovakia banning home collection of loan repayments and introducing a cap on lender fees, would hurt its business. The stock is a key holding for Andy Brough in his Schroder UK Mid 250 fund and also held by Welsey McCoy, manager of the Standard Life Investments UK Equity Unconstrained fund, according to Thomson Reuters data.
'This announcement is another blow to the viability of the company's traditional home service business model in eastern Europe, following on from the recently imposed price cap on all fee income that will be implemented in Poland from Q1 next year,' said Gary Greenwood, analyst at Shore Capital.