The gas supplier said it can give no guidance for the current year either due to the trading uncertainty.
Underlying profits fell by 23% to £1.64bn in the year to end-December, with a 31% fall in its ongoing businesses to £447mln.
Ongoing numbers exclude Direct Energy, which was sold in January for £2.7bn, and reflects the impact of Covid-19, warmer weather and low commodity prices, the group said.
Exceptional charges of £1.59bn including redundancy and pension costs of £274mln, pushed the group into a pre-tax loss of £577mln (£1.03bn loss).
British Gas Energy shed another 164,000 customers or 2%, though nearly all the net losses came in the first half of the year. The business now has 6.9mln customers.
Centrica added that a restructuring of the group that has included 5,000 job losses since the start of 2020 is on track but more change is likely.
Chris O’Shea, chief executive, said: “We have made a good start to the turnaround of Centrica, with the sale of Direct Energy now complete and our significant Group restructure on track. However, our journey to transform has only just started.”
Net debt at the year was £2.8bn, since when it has received £2.7bn for the Direct Energy sale.
Centrica said it will use part of these proceeds to redeem €750mln of hybrid debt.
The group also unveiled plans to help it become carbon net-zero by 2045 with its long-term strategy to be set out in the second half of 2021.