Conservative MPs are deciding today whether they want Prime Minister Boris Johnson to be replaced.
A vote will be held between 18:00 and 20:00 later today, with the result announced shortly afterwards.
The voting followed some Conservative MPs who have handed in letters calling for Johnson to resign.
Pressure on the prime minister has grown following the publication of details of Downing Street parties which broke COVID-19 rules.
A report, by senior civil servant Sue Gray, said many of the gatherings “should not have been allowed”.
An attempt by Conservative MPs to remove their leader is known as a vote of confidence.
For a vote to be held, at least 15 percent of Conservative MPs have to write a letter saying they no longer support their leader.
At the moment this works out as 54 MPs (out of 359) have handed in their letters.
Their letters are sent to Sir Graham Brady, the chairman of a group called the 1922 Committee, which represents them.
On Monday he said there were enough letters for a vote to take place.
BBC