After weeks of an often bad-tempered and divisive party leadership contest that pitted Truss against former finance minister Rishi Sunak, the announcement at 8.30pm on Monday Australian time will trigger the beginning of a handover from Boris Johnson.

He was forced to announce his resignation in July after months of scandal.

On Tuesday, the winner will travel to Scotland to meet the Queen, who will ask the new leader to form a government.

Truss, if appointed, will become the Conservatives’ fourth prime minister since a 2015 election. Over that period the country has been buffeted from crisis to crisis, and faces what is forecast to be a long recession triggered by sky-rocketing inflation which hit 10.1 per cent in July.

Foreign minister under Johnson, Truss, 47, has promised to act quickly to tackle Britain’s cost of living crisis, saying that within a week she will come up with a plan to tackle rising energy bills and securing future fuel supplies.

Speaking in a TV interview on Sunday she declined to give details of the measures she says will reassure millions of people who fear they will be unable to pay their fuel bills as winter approaches.

Truss signalled during her leadership campaign she would challenge convention by scrapping tax increases and cutting other levies that some economists say would fuel inflation.

That, plus a pledge to review the remit of the Bank of England while protecting its independence, has prompted some investors to dump the pound and government bonds.

The Institute for Fiscal Studies cast doubt last month on Britain’s next prime minister having room to make large, permanent tax cuts.

Truss faces a long, costly and difficult to-do list, which opposition lawmakers say is the result of 12 years of poor Conservative government.