Octopus Energy is set to hand the next UK government an early ￡3bn windfall after the company pledged it would repay all the state support it received to take over collapsed energy supplier Bulb.

Octopus confirmed to the Financial Times that it would reimburse the Treasury by September, meaning that the government will recover almost all the cost of temporarily nationalising Bulb in 2021. The bailout was at one time estimated to be the UK’s most expensive since the financial crisis, at as much as ￡6bn. Falling energy prices have slashed the final bill.

“The deal the government agreed with Octopus was fair for everyone and struck good value for taxpayers,” said Octopus, which became the largest electricity supplier in the UK, with 6.9mn customers, as a result of its state-backed takeover of Bulb. “We have already started to repay the government and it should all be complete by September,” it added.