The owner of British Gas has angered fuel poverty campaigners by offering its shareholders an extra £300m this year as millions of customers brace for rising energy bills through the winter.

Centrica expects to buy back shares worth £300m before September, meaning it will have repurchased £1.5bn in shares since November last year – equivalent to a fifth of the company’s total market value.

The company set out the shareholder windfall in a trading update weeks after the industry regulator announced that the average annual energy bill in England, Scotland and Wales would increase by £21 a year to £1,738 from January.

Bills are expected to rise again in April to £1,762 a year for a typical dual fuel consumer as a result of turbulence in the global energy markets, according to forecasts from Cornwall Insight, a respected energy consultancy. This would put the average energy bill about £740 a year higher than before the energy crisis.

Simon Francis, the coordinator of the End Fuel Poverty Coalition, said: “As millions of households spend a fourth winter in cold damp homes, the Centrica cash cow continues to deliver for the energy elite.”

He added: “This is the firm that is still under investigation by Ofgem for the prepayment meters scandal, but which has made more than £7bn in profits since the start of the energy bills crisis. Centrica’s customers who are struggling in energy debt, unable to heat their homes or cook hot meals this winter will have many other ideas about how the firm could spend this windfall in a more socially responsible way.”

Centrica has offered further share buybacks ahead of its full-year results early next year, which are expected to show a 40% slump in its earnings a share. Aarin Chiekrie, an equity analyst at Hargreaves Lansdown, said Centrica’s performance was expected to “simmer down this year, reflecting more normalised market conditions”.

Chiekrie added: “But for now, there’s still plenty of cash on hand and that’s inspired another £300m of share buybacks to be completed by September 2025.”

Cornwall warned that the government’s energy price cap could rise by an extra £20 a year on top of the £1,762 forecast for April 2025 if the government moves ahead with policy proposals that would raise costs for households. These include extra costs to compensate heavy industry for its network costs and a higher allowance for energy suppliers to recover payments which are not paid by those in energy debt.

Centrica was approached for comment.