New Prime Minister Liz Truss will unveil plans to limit energy bill rises on Thursday, spending billions to protect people from soaring prices.
Typical household energy bills could be capped at around £2,500 a year, with firms also likely to get some relief.
It is unclear how long the support will last, but the government is expected to borrow at least £100bn to pay for it.
Currently, a typical household's gas and electricity bill is due to rise from £1,971 to £3,549 in October.
Experts and charities have warned that without help on soaring energy price bills lives will be at risk this winter, as people struggle to afford basic day to day living costs.
The increase in consumers' bills follows sharp rises in wholesale gas largely due to the conflict in Ukraine, which has reduced supplies of Russian gas.
Ahead of the announcement, Ms Truss said she knew families and firms were worried about "how they are going to make ends meet this autumn and winter".
"Putin's war in Ukraine and weaponisation of gas supply in Europe is causing global prices to rise - and this has only made clearer that we must boost our long-term energy security and supply.
"We will take action immediately to help people and businesses with bills but also take decisive action to tackle the root cause of these problems, so that we are not in this position again."
To limit the amount customers' bills go up by, the government is expected to compensate energy firms for the difference between the wholesale price for gas and electricity they pay and the amount they can charge customers.
Customers will not be expected to repay the help, with the huge support package due to be funded by the government borrowing about £100bn. The final sum will depend on the cost of energy on the international energy markets - which can be extremely volatile as well as whether additional support is offered the most vulnerable households.
But Labour said the government should extend a windfall tax on gas and oil company profits to pay for the package with leader Sir Keir Starmer warning working people will be footing the bill for "vast" energy firm profits under her plans to tackle the energy crisis.
At PMQs, Sir Keir told Ms Truss "energy producers will make £170bn in excess profits over the next two years".
"Is she really telling us that she is going to leave this vast excess profits on the table and make working people foot the bill for decades to come?" the Labour leader asked.