British Gas customers increased to 7.5 million in the UK, after absorbing the customer base of Rebel Energy and Tomato Energy when those energy providers went bust.
“The environment has been challenging, and performance has varied across the business,” Mr O’Shea said.
The UK had its warmest and sunniest year on record in 2025, according to the Met Office, with an average temperature of 10.09C.
Shares in Centrica were trading down more than 7% in London on Thursday morning.