Liz Truss has promised to unveil a plan to deal with the energy crisis within a week if she becomes prime minister - though she refused to go into any detail on what this might look like.

There have been ever-louder calls in recent weeks for the government to intervene to support the most vulnerable, with energy bills set to rise to around £3,500 this winter for the average household.

The foreign secretary, widely tipped to defeat rival Rishi Sunak when the Tory leadership winner is announced on Monday, told the BBC's Sunday with Laura Kuenssberg that the UK faces "some very, very serious challenges" which will require immediate action from the government.

Pressed on what action she will take, Ms Truss said she would act quickly.

She said: "If I'm elected as prime minister, within one week I will make sure there is an announcement on how we are going to deal with the issue of energy bills and of long-term supply to put this country on the right footing for winter."

However, she said what she can't do "is tell you exactly what that announcement would be".

She added: "We still don't know the outcome of this leadership contest. So, it would be completely wrong."

Throughout the leadership campaign, Ms Truss has pledged to "start cutting taxes from day one" with a new Budget and Spending Review that would reverse April's rise in national insurance and next year's corporation tax increase from 19% to 25%.

She has faced criticism this will benefit higher earners rather than those on low incomes.

Ms Truss insisted her plan was "fair" when pressed on what more she will do.

"To look at everything through the lens of redistribution, I believe, is wrong. Because what I'm about is about growing the economy, and growing the economy benefits everybody," she said.

Although Ms Truss has hinted at more support for households, she would not say if she would freeze energy bills - as Labour has suggested - reiterating that we will find out her plan next week if she becomes prime minister.

And when asked if she will be giving people money to pay their energy bills, she said the issue is serious but her first port of call will be sorting out supply and resources in the North Sea.

She insisted she was "not being coy" by refusing to go into detail, adding: "What I've

been very clear about is that I would act immediately within a week. I understand what people are facing on energy bills."

It comes after she told the Sunday Telegraph that "sticking plasters and kicking the can down the road will not do" as a solution.

She said she would appoint a council of economic advisers to help guide her and her chancellor - within her first week in office.

"A fiscal event would follow later this month from my chancellor, with a broader package of action on the economy," she added.

Polling among Tory party members has suggested Ms Truss will win the leadership race.

Mr Sunak reiterated that he would continue as an MP if he loses the leadership election during his interview with Kuenssberg.

He also did not rule out running for the leadership again if he does not win this time.

He said: "We've just finished this campaign. So, I'd say ... I need to recover from this one. But I look forward to supporting the Conservative government in whatever capacity."

On the cost of living crisis, he said it "simply cannot be solved for everyone" but that he will target the most vulnerable in any support package.

New PM 'faces second most difficult brief since World War Two'

The interviews came as the two contenders were warned that the next prime minister faces the second most difficult brief since World War Two.

Speaking to Sky News' Sophy Ridge on Sunday, Senior Tory David Davis said whoever inherits the keys to No 10 faces the second most difficult post-war in tray, after Margaret Thatcher.

He suggested the cost of living challenge will cost tens of billions of pounds.

"I actually don't think any of the candidates, not one of them going through it, really knows quite how big this is going to be," he said.

"It's going to be on a par with the furlough scheme in terms it's going to tens of billions of costs."

Meanwhile, former chancellor Lord Philip Hammond said the incoming prime minister will need to provide help with "massive energy bills".

He said cutting taxes is "simply not the answer" to the cost of living crisis and his advice for the next incumbent of No 10 is to be "honest with the British people about the challenges we are facing in the short term".

However, when it was put to him that it sounded like he was "more on the Rishi Sunak side", he said: "I look at the bookies odds, I look at the polling and I'm pretty sure we're going to have a Truss government."

He went on to say that Ms Truss was a "formidable" chief secretary to the Treasury when he was chancellor, and that she "works very hard".

He added: "I think she can make a very good prime minister, but she must do it by being inclusive.

"She'll send a clear signal as early as Tuesday when she starts to form her cabinet.

"And it must be a cabinet that reflects the talent across the Conservative Party and sends a message to the country that this will be a government that focuses on delivery, on competence, on honesty and on applying those values in a pragmatic way."