Householders in England, Wales and Scotland will be most likely hit by further increases in their energy bills in October.
Delivering a speech at All-Energy 2022 conference in Glasgow, the boss of the energy regulator said: “The market remains highly volatile and as a result, we do expect further price increases later this year.
“I talk to customers on a regular basis, and I know how tough rising energy prices are for many households and businesses.
“For some, not being able to afford rising energy bills is literally a matter of life and death.”
Mr Brearley said gas markets remain in a “febrile” state since the Russian invasion of Ukraine.
He added: “Prices fluctuated from nearly 16 times the average price last winter at its highest to around four times what we would usually see.”