Prime Minister Boris Johnson has told Scotland's first minister that now is not the time to hold a second independence referendum.
His letter to Nicola Sturgeon came on the day dozens of his own ministers and aides called for him to quit.
Last week the FM wrote to Mr Johnson saying she was ready for talks to negotiate the powers to hold the vote.
Ms Sturgeon said she had received his reply and questioned whether it would be one of his final acts as PM.
Both the Chancellor Rishi Sunak and Health Secretary Sajid Javid resigned from their positions on Tuesday evening.
They went within minutes of each other following a row over Mr Johnson's decision to appoint Chris Pincher deputy chief whip earlier this year.
Their departures have triggered a wave of further resignations, with Kemi Badenoch, Alex Burghart, Neil O'Brien and Julia Lopez among the latest departures.
Scottish Tory MP David Duguid has said the PM's position is now "untenable", but Scottish Secretary Alister Jack gave his full backing to Mr Johnson.
At Prime Minister's Questions, Mr Johnson said he had a "colossal mandate" from the 2019 election and would "keep going".
Question 'clearly answered'
On Wednesday afternoon it emerged that the prime minister had sent a letter to Ms Sturgeon saying: "I have carefully considered the arguments you set out for a transfer of power from the UK parliament to the Scottish parliament to hold another referendum on independence.
"As our country faces unprecedented challenges at home and abroad I cannot agree that now is the time to return to a question which was clearly answered by the people of Scotland in 2014."
Before the Scottish Parliament went into summer recess last week, Ms Sturgeon addressed MSPs proposing 19 October 2023 as the date for another referendum on independence.
She said the question would be the same as in the last referendum in 2014: "Should Scotland be an independent country?"
However, in order to hold a legal referendum Scotland requires special powers to be granted by Westminster.
Mr Johnson's letter, dated 6 July, makes clear that it will not happen under his leadership.
Ms Sturgeon tweeted her response, saying: "Just received this from Johnson (one of his last acts as PM?).
"To be clear, Scotland will have the opportunity to choose independence - I hope in a referendum on 19 October 2023 but, if not, through a general election. Scottish democracy will not be a prisoner of this or any PM."
In his letter, Mr Johnson highlighted the co-operation between both governments on measures to ease the cost of living, close collaboration to tackle the Covid-19 pandemic, and ongoing support for the UK's response to the war in Ukraine.
He concluded: "On all fronts, we stand to achieve so much more for the people we serve by continuing to work together as partners. Thank you, once again, for writing to me."