Centrica lost almost a fifth of its value in early trading after posting an £849m pre-tax loss for 2019.
In 2018 the group had recorded a profit of £987 million.
One-off charges totalling £1.1bn hit numbers hard and the near-term outlook remains grim for upstream operations.
Spirit Energy, the group’s North Sea oil and gas business now up for sale, incurred an impairment of £476 million. Exposure to the Dungeness B and Hunterston D nuclear plants, both responsible for power outages during the year, brought a further hit while some £356 million of redundancy and restructuring costs weighed heavy.
While domestic energy supply customer losses slowed, the company claimed the price cap cost it £300m.
Outgoing CEO Iain Conn suggested that, stripping away external factors, the core businesses remained stable relative to 2018.
The UK business energy division posted growth in customer numbers (up 7 per cent to 342,000), revenue and adjusted operating profit.
Full results here.