London, UK - New Prime Minister Liz Truss said the UK would "ride out the storm" as she prepared a relief package to help households cope with soaring energy costs.

In her first speech in the role, she acknowledged the economic headwinds facing the country but promised action this week to help with energy bills.

In her first address as prime minister, Truss said: "I'm confident that together we can ride out the storm, we can rebuild our economy, and we can become the modern brilliant Britain that I know we can be. This is our vital mission to ensure opportunity and prosperity for all people and future generations. I'm determined to deliver."

Truss officially became prime minister after an audience with Queen Elizabeth II at Balmoral Castle in Scotland. The queen shortly before had received Boris Johnson's resignation.

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While Johnson had delivered his farewell speech in sunshine, Truss had to dodge torrential showers in central London for her address from a podium outside the black door of her new office and residence, 10 Downing Street.

She vowed to create an "aspiration nation," promising to tackle the issues that have been holding Britain back for years by building "roads, homes and broadband faster."

In an echo of Winston Churchill, she promised "action this day" to deliver her plans to transform the country.

But in an acknowledgement of the immediate problem facing households across the country, she said: "I will take action this week to deal with energy bills and to secure our future energy supply."

As well as dealing with the energy crisis, Truss said her early priorities included "a bold plan to grow the economy through tax cuts and reform" and "get Britain working again."

She also promised to "put our health service on a firm footing" so "people can get doctor's appointments and the NHS services they need," referring to the National Health Service.

Truss said: "We shouldn't be daunted by the challenges we face. As strong as the storm may be, I know that the British people are stronger. Our country was built by people who get things done. We have huge reserves of talent, of energy and determination."

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Shortly after finishing her speech in Downing Street, Truss headed to Parliament, where she began a cull of ministers who had been loyal to her Conservative leadership rival Rishi Sunak.

Among the casualties were deputy prime minister and justice secretary Dominic Raab, transport secretary Grant Shapps, and health secretary Steve Barclay.

Truss is expected to reward allies, with Kwasi Kwarteng tipped to take the key post of chancellor and Therese Coffey in line to become deputy prime minister.

In her speech outside No. 10, Truss paid tribute to her predecessor, saying that "Boris Johnson delivered Brexit, the Covid vaccine, and stood up to Russian aggression."

"History will see him as a hugely consequential prime minister."

In his own address before leaving Downing Street for the final time as prime minister, Johnson called for Conservatives to unite behind his successor.

Johnson said, "I will be offering this government nothing but my most fervent support," calling for Conservatives to back the new leader at a "tough time for the economy."

He said his career was now like a booster rocket "that has fulfilled its function, and I will now be gently re-entering the atmosphere and splashing down invisibly in some remote and obscure corner of the Pacific."

US President Joe Biden offered his congratulations to the Truss, saying he looked forward to "deepening the special relationship between our countries and working in close cooperation on global challenges, including continued support for Ukraine as it defends itself against Russian aggression."

But the trans-Atlantic relationship could be strained if Truss pushes ahead with the plan to override parts of Northern Ireland's Brexit deal. Biden is proud of his Irish roots and takes a keen interest in the issue.