Ruth Davidson is on the verge of quitting as leader of the Scottish Conservatives, BBC Scotland understands.
Ms Davidson has been deeply unhappy with the prime minister’s pursuit of a possible no-deal Brexit.
She is said to be considering her position, with a statement on her future likely to be made on Thursday.
Ms Davidson, who gave birth to a son in October of last year, has been leader of the party since November 2011.
Sources have told the BBC’s political editor, Laura Kuennsberg, that Ms Davidson’s decision was based on a mixture of personal and political factors which have been building over recent months.
And they said it was not a direct result of the announcement by Mr Johnson that he wants to suspend parliament in September – only a few weeks before the Brexit deadline of 31 October.
Ms Davidson backed Remain ahead of the EU referendum, and famously clashed with Mr Johnson in a live TV debate before the vote.
She publicly backed opponents of Mr Johnson in the Conservative leadership contest, and has previously said she would not support a no-deal Brexit.
The Scottish Conservatives are the second-largest party in the Scottish Parliament, and have 13 MPs at Westminster.