London stocks tipped into the red shortly before the close after a slump on Wall Street and a fall in BT's share price impacted the FTSE.
BT was one of the day's heaviest fallers after Patrick Drahi's fairly modest increase in his stake calmed takeover talk, although it was pipped to the bottom spot of the FTSE by Rentokil - which dropped after sealing a takeover.
The FTSE 100 closed 12.8 points, or 0.18%, lower at 7,218.64 on Tuesday.
Danni Hewson, AJ Bell financial analyst, said: "London markets have had an odd sort of day - some of Monday's big Covid losers like IAG and Trainline have recouped some of their losses but there's been plenty of other disappointments to trouble investors.
"Initial excitement about news that Rentokil was pushing into the US by snapping up fellow terminators Terminex died quickly, and impressively.
"Then there's the long-awaited move by Patrick Drahi. He's added to his BT share count but with a warning from a Government spokesperson ringing in the ears, a full-on bid, at least for the foreseeable future, looks incredibly unlikely."
Elsewhere in Europe, the other key markets also fell over growing concerns over the rapid rate at which Omicron is spreading across the continent.
The German Dax decreased by 1.08% and the French Cac decreased by 0.69%.
Across the Atlantic, US tech shares fell on the back of continued inflation woes.
Meanwhile, sterling was cautious ahead of a potentially intriguing set of inflation figures on Wednesday and the latest Bank of England rate decision on Thursday.
The pound moved 0.05% lower versus the US dollar at 1.322, and decreased 0.05% against the euro at 1.173.
In company news, Ocado rebounded after the online retail firm learned overnight that it had won a court battle in the US, where it was accused of patent infringement by rival AutoStore.
It kept optimism high among investors despite the firm revealing that cost pressures, driver and warehouse worker shortages and more customers heading back to offices prior to the recent Covid rule changes all contributed to falling sales.
Shares in the company climbed by 87p to 1,678p as a result.
Fashion brand Joules tumbled heavily after it warned that higher costs and stock delays are expected to weigh on its profits into next year.
It saw shares slide by 50p to 145p after it said it expects pre-tax profit of between £2 million and £2.5 million for the latest period, representing a decline from £3.7 million in the previous financial year.
Rentokil plunged to the foot of the FTSE after shareholders were left unimpressed by its mammoth 6.7 billion US dollar (£5.1 billion) deal to buy American rival Terminix in a move that will see it become the biggest firm in the market worldwide. Shares finished 76.8p lower at 547.6p.
The price of oil dropped back as the spread of Omicron sparks uncertainty over travel.
Brent crude decreased 2.19% at 72.76 dollars per barrel when the London markets closed.
The biggest risers on the FTSE 100 were Ocado, up 87p at 1,678p, Evraz, up 14p at 606.6p, British Land, up 11.6p at 514.6p, and Rio Tinto, up 106p at 4,854p.
The biggest fallers were Rentokil, down 76.8p at 547.6p, BT Group, down 7.5p at 167.35p, Darktrace, down 15.8p at 376p, and Spirax-Sarco, down 605p at 15,445p.
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