Centrica's 35% slump in full-year operating profit pushed its share price down more than 15%, making it the biggest faller on today's FTSE 100. The index itself ended the day down 1.09% or 82.34 points at 7,452.03, while the FTSE 250 fell 0.55% or 119.58 points to 21,673.90.
Global financial markets are reacting to yesterday's sharp increase in confirmed new coronavirus cases, which rose 15,000 in a day, while the death toll rose by 242.
The escalation is "applying the brake on stock market gains", says Neil Wilson of Markets.com.
The Asia markets weakened slightly overnight, with Hong Kong down 0.5% and the Shanghai Composite down 0.7%.
Meanwhile, in the UK, the FTSE 100 has been pulled down by some "pretty shoddy numbers" from Centrica, which has fallen 16%.
"This is the sort of thing to jolt complacent stock markets into a greater sense of the risks this outbreak poses," Mr Wilson says.
"The increase is largely down to a new way of recording cases, but it nonetheless puts into sharp focus for traders the extent of the virus."
BBC Radio 4
British Gas owner Centrica reported its results for 2019 this morning.
Due to lower prices of natural gas and the introduction of the energy price cap, it saw a 35% slump in full-year operating profit.
Britain's largest energy supplier said adjusted operating profit for the year ended 31 December fell to £901m from £1.39bn pounds a year earlier.
Iain Conn, chief executive of Centrica, called 2019 a "difficult year, with the first year of the implementation of the price cap".
He told the BBC's Today programme that there were however some bright spots: "Very importantly, our core customer business did well, with profits improving by £298m. That nearly offset the impact seen by the introduction of the price cap."
As we reported earlier, NMC Health has had a mixed day with news of a possible takeover and the departure of its founder.
The news pleased the market sending its shares leaping by a third to lead the FTSE 100 risers. It closed at 926.20 after climbing 32.31% during the day.
Other climbers included housebuilder Barrett Developments, which added 3.05%, British Land (+1.93%), Next (+1.69%) and Land Securities (+1.64%).
British Gas owner Centrica led the fallers after closing at 82.68, down 2.89%.
Other losers included Carnival (-2.25%), Evraz (-2.09%), Hikma Pharmaceuticals (-1.73%), Glencore (-1.54%) and Rio Tinto (-1.54%).
British Gas owner Centrica has revealed it has lost another 107,000 household accounts, as it also upped its annual cost savings by £50m.
But the UK's biggest gas and electricity supplier said it had eased the rate of customer losses, which were lower than the first half of the year, when it shed 178,000 accounts.
The group also said it now expects annual cost savings of £300m from the previous target of £250m, while it is trimming planned investment spend by £100m to about £800m.
Centrica is already axing up to 2,000 jobs over 2019 as part of overall aims to save £1bn by 2022, but gave assurances that the increased cost savings this year will not lead to further staff cuts.
In news of another court case involving a former taxpayer-owned business, British Gas owner Centrica, has won a court battle with energy regulator Ofgem.
The energy supplier took legal action after the regulator announced a surprise change to the methodology used to set the energy price cap.
Centrica said the late change in determining fair energy prices for 11m homes knowingly underestimated the cost of supplying energy last winter, and would lead to an unexpected one-off cost increase of £70m for British Gas.
The case revolved around the way the watchdog calculated wholesale costs under the cap.
Ofgem said it was disappointed by the judgment but its energy price cap would remain fundamentally unchanged.
The FTSE 100 is trading 0.20% lower at 7,411.02.
Whitbread remains the biggest faller with its share price down 4.5% at £42.63.
British Gas-owner Centrica is now leading the FTSE 100 risers, up 2.1% at 75.02p.
FTSE 250 is down 0.24% at 19,922.73