The FTSE 100 lost 1pc, as trade concerns weighed on Asia-exposed financial stocks like HSBC, while oil majors Shell and BP also slipped on supply concerns.
The FTSE 250 gave up 0.5pc, with losses in all sectors, though pub operator Mitchells & Butlers outperformed after reporting a higher profit.
Worries over U.S.-China trade escalated as President Donald Trump threatened to raise tariffs on imports if no deal was reached, while nerves were jangled further after the U.S. Senate passed legislation backing protesters in Hong Kong, which drew condemnation from Beijing.
That spurred a sell-off in most trade-sensitive sectors, including miners, and encouraged buying of so-called defensive stocks like healthcare.
"Given that the U.S. Senate has just passed legislation in support of the Hong Kong protests, such a move threatens to drive a wedge into ongoing negotiations while potentially raising the barrier to a trade deal," Han Tan, market analyst at FXTM said.
Shares in Aviva Plc fell 4pc. The insurer, which analysts and investors say is struggling for direction since replacing its top boss, said it was restructuring its business and selling its stake in its Hong Kong unit.
Domestic stocks, which have benefited from polls indicating a likely Conservative victory in the upcoming election, weakened after three sessions, but still outperformed the broader European benchmark.
Markets are viewing a prospective Tory victory as a positive on hopes that Prime Minister Boris Johnson, with a majority in parliament, will be able to reduce uncertainty by delivering Brexit by the Jan. 31 deadline.
With less than a month to go before the ballot, Johnson on Tuesday doubled down on his Brexit promise in a debate with his main rival, Labour Party leader Jeremy Corbyn.
Other news-driven moves saw AIM-listed Fevertree, which slid in early trading, recoup to rise as much as 8pc.
Analysts indicated the market was seemingly shrugging off the tonic water maker's revenue warning to focus on sales growth in the U.S.