Traders felt the hangover from their week-long vaccine celebration on Tuesday as London's top index closed down.
The FTSE 100 lost 0.9%, or 55.96 points, to 6,365.33.
It came a day after Moderna announced a strong set of results from its vaccine trials, showing that it could protect 95% of people from the coronavirus.
The news added to a week of celebrations, after Pfizer announced its results last month.
But with no new vaccines to toast on Tuesday, global markets were more subdued.
"Remembering that the vaccine isn't actually here just yet, the markets accelerated their retreat this Tuesday afternoon," said Spreadex analyst Connor Campbell.
In New York, the S&P 500 fell by 0.4%, while the Dow Jones had lost 0.6% of its value shortly after markets closed in Europe.
On closing, the European markets were in less celebratory mood than they have been, though avoided a day as bad as in London.
The Cac in Paris rose by 0.2%, while Frankfurt's Dax stayed more or less flat.
The FTSE was also hit by a strong pound, which surged 0.4% against the dollar to 1.3247, and gained 0.3% when buying euros, at 1.1166, on hopes of a possible Brexit deal.
Mr Campbell said: "As Irish Taoiseach Micheal Martin stated that both sides could see the 'landing zones' around an agreement, and Bloomberg reported that a breakthrough could be announced on Monday, sterling shot up."
Vodafone was among the stragglers on the FTSE 100 a day after pulling into the index's top five on Monday. It announced that the mast businesses it plans to spin off next year will pay out major dividends. Shares fell by 4.1%.
Not far behind among the worst performers for the day was IAG, which owns British Airways. The carrier had said on Tuesday that it will test passengers for coronavirus as part of a voluntary trial that it hopes will prove the UK's quarantine policy can be lifted. Shares dropped 3.3% in the parent company.
Its budget carrier rival easyJet also fared poorly, losing 1.9% of its value, after crashing into its first ever loss in a set of full-year accounts.
On the other end of the spectrum was Imperial Brands, which became the FTSE 100's second best performer after it reported that tobacco revenue rose 1.8% in the last year.
And Sainsbury's news that it had more than one suitor that had expressed an interest in its banking arm sent its shares up by 1.7%, while Johnson Service Group rose 1% after it revealed around 1,550 job cuts.
The price of Brent crude oil dropped by 0.9% per barrel to 43.41 US dollars.
The biggest risers on the FTSE 100 were Intermediate Capital Group, up 123p to 1,689p, Imperial Brands, up 103p to 1,505.5p, Taylor Wimpey, up 8.7p to 159p, Barratt Developments, up 20.2p to 654.4p, and Homeserve, up 30p to 1,267p.
The biggest fallers on the FTSE 100 were Antofagasta, down 50p to 1,106.5p, Vodafone, down 5.24p to 122.54p, London Stock Exchange, down 328p to 7,936p, Hikma, down 97p to 2,547p, and Experian, down 102p to 2,893p.
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