Sliding oil prices and a return to April lows for sterling left UK stocks vulnerable to volatile moves on Wednesday, with energy stocks and banks exerting downside pressure.
Nymex West Texas Intermediate, the US crude benchmark, slid into bear market territory on Tuesday, having fallen 20% from its last cyclical peak in May.
ICE Brent crude, the global oil benchmark, has fallen 18% since its last cyclical peak.
On Wednesday, WTI was down 0.2% at $43.43 a barrel, its lowest since November, while Brent was down 0.4% at $45.84 a barrel and also a November low.
Fears of oversupply have dogged the oil market for more than three years and even moves by Opec, in league with Russia and other non-cartel members, to limit supply have failed to put a long-term floor under prices.
Reports of an unexpected supply increase from Libya – an Opec member – have put oil prices under pressure in the past couple of trading sessions.
"Investors who were ardently waiting for signs of Opec’s strategy to balance the saturated markets are starting to lose patience, which is reflected in the bearish price action of oil," said Lukman Otunuga, research analyst at FXTM.
Growth fears hit pound
Sterling, meanwhile, slipped to its lowest levels in seven weeks on rising concerns that protracted Brexit negotiations will undermine UK growth.