Britain's outgoing Prime Minister Liz Truss said on Tuesday that her government had acted "urgently and decisively" to help hard-working families and provided assistance to thousands of businesses to avoid bankruptcy.

Truss was speaking after chairing her final Cabinet meeting at 10 Downing Street before heading towards Buckingham Palace to formally tender her resignation to King Charles.

In her farewell speech, Truss said it was "a huge honour" to be prime minister and to lead the nation in mourning the death of Queen Elizabeth II and welcoming the accession of King Charles III.

Truss, who stepped down last Thursday after 45 days in office becoming Britain's shortest serving Prime Minister, said that her government had acted "urgently and decisively" to help hard-working families.

She said she had helped thousands of businesses to avoid bankruptcy, and taken back energy independence so we're "no longer reliant on malign foreign powers".

She will hand over power to Rishi Sunak, who was elected unopposed as the new leader of the governing Conservative Party on Diwali.

The 42-year-old former Chancellor of Exchequer, a devout Hindu, will enter 10 Downing Street to be the youngest British prime minister in 210 years after his audience with King Charles III at Buckingham Palace, which is likely to be on Tuesday. He will be the first Hindu Prime Minister of Indian heritage in the UK.

Truss on Monday congratulated Sunak on being appointed as Leader of the Conservative Party and next Prime Minister, saying "You have my full support."

The outgoing prime minister won on a mandate to slash taxes to spark economic growth, but she was forced to U-turn on almost all of her economic policies after her mini-budget sent the markets into financial turmoil and the Pound Sterling crashing.

Sunak had famously challenged Truss' plans as "fairy-tale economics", and his supporters repeatedly pointed out how he had got the big calls right and was therefore the right candidate to restore economic credibility.