Liz Truss (C) speaks to her husband Hugh O'Leary (R), next to Rishi Sunak (L) during the announcement of the winner of the Conservative Party leadership contest in London on Monday. AFP

The foreign secretary, who will replace Boris Johnson as PM on Tuesday, walked past her rival without acknowledging him on her way to give her victory speech.

It comes after Sunak last month effectively ruled out serving in a Truss cabinet, during what was sometimes a bad-tempered leadership race. Sunak had rubbished Truss's economic policies and warned she risked provoking an inflationary spiral with unfunded tax cuts.

Truss acknowledged her rival in passing at the podium, telling her audience: “I'd like to pay tribute to my fellow candidates, particularly Rishi Sunak. It's been a hard-fought campaign.”

The margin of victory between the two candidates was ultimately far narrower than had originally been predicted by pollsters.

Truss was ultimately elected by the lowest ever margin for a Tory leader under the current system, with 57 per cent of the vote to 43 per cent for Sunak.

As Truss stood up to give her victory speech she was afforded a light pat on the back by her husband, who was sitting next to her – though she did not acknowledge him in return.