The London markets tumbled as increased health concerns weighed on equity benchmarks across the globe.
UK indices were particularly impacted by comments made by US health officials on Thursday evening, moving them further into the red than their main European counterparts.
The FTSE 100 closed 83.06 points lower at 6,157.3p at the end of trading on Friday.
David Madden, market analyst at CMC Markets UK, said: “Yesterday, Dr Anthony Fauci, a US health official, warned that Covid-19 might have mutated, and it might be able to spread at a faster rate.
“Stocks enjoyed a big rally yesterday on the back of the optimism about a possible Covid-19 vaccine – that is being developed by Pfizer and BioNTech – and the very well-received US non-farm payrolls report.
“All of the gains the FTSE 100 made yesterday have been lost today on renewed health fears.”
The other major European markets were also deflated as the latest warnings from the US over the continuing impact of the virus pressed down on traders.
The German Dax decreased by 0.64%, while the French Cac moved 0.84% lower.
It was a quiet day across the Atlantic as trading was shut for the Independence Day holiday.
Meanwhile sterling dipped slightly against the euro and dollar after the latest set of UK service sector data for June was reported roughly in line with expectations, as its recent decline slowed down sharply.
The value of the pound fell 0.04% versus the US dollar at 1.246 and was down 0.09% against the euro at 1.108.
A number of airliners, including EasyJet and Wizz Air, pushed higher during the trading session after the UK Government published its list of countries and territories where English holidaymakers can visit without self-isolating on their return.
In company news, commercial landlord Landsec saw shares improve after it promised to start paying out to shareholders again and revealed that post-lockdown shoppers are spending more.
The company said the average spend at its English shopping centres jumped by 22% in the two weeks after lockdown restrictions on non-essential shops were eased, compared with last year. Shares were 3p higher at 578p on Friday.
Shares in troubled subprime lender Amigo Loans jumped after it said it will have until the end of October to clear a backlog of at least 9,000 complaints that it had originally promised to get out of the way a week ago.
The lender said that it had agreed a new deadline with the City watchdog to allow it time to deal with customers. It moved 5.22p higher to 13.72p at the close of play.
Elsewhere, shares in Rolls-Royce slid following reports that the engineering giant was eyeing up a potential fundraiser to shore up its finances. Shares dropped by 29.3p to 263.2p.
The price of oil was largely flat as health concerns sapped confidence out of the energy market, as concerns over demand continued to keep prices down.
The price of a barrel of Brent crude oil decreased by 0.02% to 42.72 US dollars.
The biggest risers on the FTSE 100 were Whitbread, up 38p at 2,387p, Fresnillo, up 12p at 855.6p, Just Eat Takeaway, up 112p at 8,600p, and Homeserve, up 10p at 1,287p.
The biggest fallers of the day were Rolls-Royce, down 29.3p at 263.2p, Next, down 232p at 4,798p, Taylor Wimpey, down 6.25p at 137p, and Barratt Developments, down 14.5p at 490.3p.