The FTSE 100 index fell 135.2 points to 5,952 - the lowest level since late September.
Firms with interests in South Africa continued to suffer after the rand hit a record low following the sacking of the country's finance minister.
Financial services group Old Mutual, which fell nearly 11% on Thursday, closed down a further 10.6%.
Packaging company Mondi, which has a South African division, fell 3.1%.
On the FTSE 250 index, Investec, which plunged on Thursday, lost a further 10.8% to 419p.
Mining shares continued their recent dismal run, with commodity prices hitting multi-year lows this week.
Shares in Anglo American, which announced a huge restructuring programme on Tuesday, fell a further 8% to 292.9p after Goldman Sachs cut its price target for the firm to 280p from 430p.
BHP Billliton closed 5.3% lower, while Shell shed 4.8%.
Goldman Sachs also cut its price target for Sports Direct. The retailer's shares had dived 11% on Thursday after its half-year results fell short of expectations, and they were down a further 1.1% on Friday.
On the currency markets, the pound rose half a cent against the dollar to $1.5214, and was down a fifth of a cent against the euro at €1.3843.
