Keir Starmer today broke cover over the cost-of-living crisis and promised to publish a "comprehensive" plan of action on Monday.
The Labour leader returned from holiday as alarming fresh predictions emerged that annual bills could top £5,000 next Spring.
Labour has faced criticism for not spelling out its full plan to tackle soaring bills, while Gordon Brown proposed a detailed package that included cancelling October's huge price cap rise and renationalising firms that fail to keep prices low.
By comparison Labour has so far vowed to scrap VAT on bills and even out inequality between pre-paid meters and direct debits - saving about £200 and £100 on a bill of £4,000.
Labour would also reimburse energy firms for the cost of cutting pre-paid bills, costing around £113m between October and March. The party insists this would be paid for by closing "gaps" in the Tories' energy windfall tax.
Interviewed today for the first time this week, Sir Keir insisted the party had been "leading" on the cost-of-living crisis for a year before this week's bill projections.
He said: "On Monday I'm going to be setting out a comprehensive set of proposals, a plan for how we handle the upcoming costs in the autumn.
"While what you've had from the Conservative Party is two leadership candidates arguing with each other about just how appalling their record in government has been, and a Prime Minister who's a lame duck.
"He recognises there's a problem and he's not prepared to do anything about it."
The Labour leader plans a whirlwind round of interviews to spell out the plan next week but will not give a speech, it's understood.
It came hours after Boris Johnson broke cover with his first interview since he returned from his Slovenian luxury honeymoon.
The Prime Minister admitted what he's promised is not enough and "extra cash" will be needed.
In a clear signal to next PM Rishi Sunak or Liz Truss he added: "There will be more announcements in September - and those will address the key pinch points in October and January."
But he refused to set out a plan himself, saying it was a job for his successor.
The latest forecast showed the £1,971 annual price cap on bills could hit £3,628 in October, £4,538 in January and £5,277 in April.
Earlier shadow business secretary Jonathan Reynolds defended his boss, telling LBC: "He is working like he does every day on the job. I honestly cannot fault the man's work ethic."
Mr Reynolds added: "I think he is spending some time with his family and that is the right thing to do.
"But I cannot fault the man's work ethic, he has been relentless since he became leader of the opposition."
Sir Keir told reporters during a visit to Scotland: "It was nearly 12 months ago now on energy bills that we proposed insulation of homes, a massive project to bring down the costs.
"In January we said there should be a windfall tax, it took the Government five months to catch up with that idea and implement it. We also said that VAT should be taken off energy bills - Rishi Sunak is only just now recognising that Labour got it right again."
"So, for the best part of 12 months, Labour has been absolutely leading on this issue."
Earlier the Shadow Chancellor said Labour will cut energy bills for the 4million poorest customers using prepayment meters.
Rachel Reeves said the party would end the “unjustifiable” practice of charging people who pay by pre-payment meter more than those who have a direct debit.
However, the change would not be nearly enough to stop bills soaring overall.
On the current price cap - set to rise in October - the difference is worth only £46 a year.
Currently the price cap is £1,971 for direct debit customers and £2,017 for those who pre-pay for energy.
Labour said the saving would likely be £84 a year from October and £100 a year from March, when bills skyrocket to more than £4,200.
