LIZ Truss will be Britain's next Prime Minister after she today vanquished Rishi Sunak to be crowned the new Tory leader.

She will succeed Boris Johnson as the country's 56th premier after being formally appointed by the Queen at Balmoral tomorrow.

And work and pensions minister Theresa Coffey suggested Ms Truss' new Cabinet would also be appointed on Tuesday.

Asked if she's expecting to keep her post in the Cabinet, Ms Coffey said: "That is up to the leader of the party, and soon-to-be prime minister. All the posts will be confirmed tomorrow."

The Foreign Secretary easily saw off former Chancellor Rishi Sunak beating him by 81,325 votes to 60,399 - a 57.4 per cent majority.

Ms Truss remained the frontrunner throughout the bruising summer contest, streaking ahead in the polls by wooing grassroots Tory members with her promise of bumper tax cuts.

But she will enter Downing Street with the most daunting economic circumstances since the 1970s as inflation bites.

Giving her victory speech in Westminster, the PM elect said: "I will deliver a bold plan to cut taxes and grow our economy. I will deliver on the energy crisis dealing with people's energy bills, but also dealing with the long term issues we have on energy supply."

She is expected to announce her energy plans within the next week to cushion Brits from crippling bill hikes.