The Scottish Tory leader gave her Westminster colleagues a severe telling off after the Prime Minister’s official Twitter account made the cock-up on Tuesday night.
It came after May and Scottish First Minister Nicola Sturgeon met in Downing Street for crunch talks over Brexit.
After the meeting May’s account tweeted : “The UK and Scotland must continue to work together to ensure businesses and consumers have the certainty they need as we leave the EU.”
Delighted Scottish nationalists seized on the wording, which suggested Scotland and the UK are already separate entities.
And Spectator journalist Isabel Hardman joked: “It’s been a busy few days but I’m amazed we all missed Scotland leaving the UK in the midst of it.”
But Davidson – who played a key role in the 2014 campaign to keep Scotland in the UK – was left fuming.
A source close to the Tory leader said: “Ruth hit the roof when the tweet was posted.
“It clearly wasn’t the PM’s fault but Ruth made it clear to Number 10 that this kind of language only plays into the hands of the SNP by making it sound as if Scotland is a separate country to the UK.
“There was a referendum about this. I don’t think it’ll be happening again.”
Meanwhile, a Downing Street source told the Record there is now a “brutal blame game” going on in Number 10 over who was responsible for the blunder.
It’s understood the Tweet was meant to refer to the need for the “Scottish and UK Governments” to work together on Brexit.
An SNP source quipped: “This tweet is the highlight of May’s premiership thus far.”
The “cordial” meeting in Downing Street saw Sturgeon inch closer towards striking a Brexit devolution deal with May.
The First Minister said she was “hopeful” of a breakthrough in the deadlock over whether Brussels powers should be devolved straight to Scotland or rest in Westminster after Brexit.
Speaking to reporters as she emerged from a 30 minute meeting on Tuesday night, the FM said she and the Prime Minister had reached “a better understanding of each other’s positions”.
The sign of a thaw came as the EU Withdrawal Bill returned to the Commons to begin its line by line scrutiny and crucial votes.
Both Scottish and Welsh governments continue to refuse consent for the bill unless Westminster surrenders on a so-called “power grab” of EU responsibilities and devolve them directly to Edinburgh and Cardiff.
Sturgeon has said the bill is still unacceptable in its current form.