At least 160 British lawmakers from Prime Minister Boris Johnson's Conservative Party had publicly indicated support for him ahead of a confidence vote over his leadership on Monday, a Reuters tally showed.

A total of 180 votes would be enough to ensure he survives the leadership challenge. The ballot will be secret and there is no guarantee lawmakers will vote in line with their public statements.

The vote is due to commence at 6 pm (1700 GMT), with a result expected at 9 pm.

Johnson, who scored a sweeping election victory in 2019, has been under increasing pressure after he and staff held alcohol-fuelled parties in his Downing Street office and residence when Britain was under strict lockdowns due to Covid-19.