European markets remained unmoved by Monday's events, as a strong pound did not do enough to put a serious dent in the FTSE 100.
London's top market ended the day down just 5.84 points to 6026.25, a 0.1% fall.
British Airways owner IAG led the pack lower as its shares lost more than 30% of their value because of a rights issue.
It was a technical drop after the airline launched a £2.5 billion issue of shares last week.
It was joined towards the bottom by natural resource giants including Polymetal, Fresnillo, BP, Shell and Antofagasta, which often take a hit when the pound soars.
It was news of a possible revolt against Boris Johnson's plans to break international law that helped sterling reverse some of the losses it racked up last week.
The currency jumped by two-thirds of a per cent to 1.2878 against the dollar, and by one-third to 1.0842 when buying a euro.
"Reports of Tory opposition to the law-breaking UK Internal Market Bill, and BNP Paribas's claim that a no-deal Brexit isn't 'inevitable', gave the currency a reason to move higher," said Connor Campbell, an analyst at Spreadex.
Micheal Hewson, at CMC Markets, said that an early rise on Monday tapered off during the afternoon even as big-ticket mergers, such as those of ARM and TikTok excited traders.
"The rising tide of coronavirus cases across the UK and Europe and the resultant tightening of restrictions, along with the announcement by the CEO of the world's largest vaccine maker, the Serum Institute of India, that it could take until 2024 before everyone is inoculated has helped to temper some of this morning's early enthusiasm," he said.
In the US things were more positive as the S&P 500 added 1.7% and the Dow Jones rose 1.3%.
Monday's biggest listed company news in the UK came from G4S which rejected an unsolicited £2.96 billion potential bid from Canada's GardaWorld. Shares ended the day up by a quarter at 182.45p, below the 190p offer price.
Shares in Vodafone Group closed down by half a per cent on the news that it plans to sell its stake in Vodafone Egypt for 2.4 billion US dollars (£1.9 billion). A potential buyer is far through its due diligence process, Vodafone said.
The cost of a barrel of Brent crude oil dropped by 0.4% to $39.66.
The biggest risers on the FTSE 100 were Ocado, up 89p to 2,355p, Compass Group, up 40p to 1,313.5p, Land Securities, up 14.1p to 543.9p, British Land, up 8.6p to 347.3p, and BAE Systems, up 12.2p to 520.2p.
The biggest fallers on the FTSE 100 were IAG, down 59.85p to 134.35p, Polymetal, down 75.5p to 1,933.5p, Fresnillo, down 48.5p to 1,303.5p, BP, down 4.95p to 257.1p, and Intermediate Capital Group, down 23p to 1,234p .
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