The Queen will break with tradition to appoint Britain’s new prime minister at her Balmoral Castle residence in Scotland rather than at Buckingham Palace in London, due to the 96-year-old monarch’s mobility issues.

A Buckingham Palace spokesperson said on Wednesday that the Queen would meet outgoing Prime Minister Boris Johnson as well as his successor on September 6 at Balmoral, where the monarch spends her summers.

She will have an audience with Britain’s new leader – either Foreign Secretary Liz Truss or former finance minister Rishi Sunak – shortly after meeting Mr Johnson, the spokesperson said.

The result of the Conservative Party leadership contest to succeed Mr Johnson will be announced on September 5, with polls making Ms Truss the clear frontrunner.

The decision to have the audiences at Balmoral was taken to provide certainty for the new prime minister’s diary and avoid having to make any last-minute changes were the Queen to experience mobility issues, a palace source said.

Britain’s monarch, as head of state, traditionally appoints the new prime minister following an audience at Buckingham Palace, part of the drama of the day, when television cameras and helicopters follow official cars pulling into the palace grounds.

Every British leader has been appointed at Buckingham Palace since the reign of Queen Victoria except on one occasion, the BBC said, citing constitutional expert Vernon Bogdanor.

The Queen, who has had 14 prime ministers during her reign, has faced ‘‘episodic mobility issues’’ in recent months, forcing her to reduce her public appearances.

She also spent a night in hospital last October for an unspecified illness.

In June, however, she appeared on the balcony of Buckingham Palace alongside her family to wave to cheering crowds at a celebration marking her record-breaking 70 years on the British throne.

At the Commonwealth Games in Birmingham last month, her son and heir to the throne Prince Charles delivered a speech on her behalf.

-Reuters