Scotland's First Minister Nicola Sturgeon has written to the British prime minister formally requesting talks to facilitate a second Scottish independence referendum.
The full text of the letter will be made public on Friday, however it has been reported that Ms Sturgeon will urge Mrs May to make a start on transferring the power to have a referendum.
She will say time is tight if the process for holding it is to be squeezed into her preferred timetable of 18 months.
It is a request that Theresa May will almost certainly reject.
Mrs May has consistently taken the line that "now is not the time" for a second independence referendum.
There's nothing to suggest she will take a different view when Ms Sturgeon's letter, in PDF format, drops into the Downing Street inbox.
Whilst Scottish Government officials drafted several versions of the letter for their First Minister, Ms Sturgeon crafted the final version herself inside her private study on the upper floors of her official Bute House residence in Edinburgh.
Tomorrow's front page: Now THIS letter's ours! Sturgeon signs request for indyref2 after Tories launch Westminster power grab pic.twitter.com/m2quzC0we1
— The National (@ScotNational) March 30, 2017
A hard copy of the letter will be sent to Downing Street, with a PDF file emailed as an attachment.
Mrs May and Ms Sturgeon met earlier this week in Glasgow as the First Minister continued to press her case for another referendum.
Ms Sturgeon described it as "reasonably cordial" and said her hope for another vote in 18 months to two years' time was realistic because the PM had told her the terms of a Brexit deal should be clear by then.
However, in a speech before the meeting, Mrs May hailed the United Kingdom as an "unstoppable force."
The PM is sticking to her belief that a vote in the next two years would be "unfair" on people in Scotland because not all the terms about life outside EU will be finalised.