The prime minister has said completely unambiguously that she will reject a demand from the First Minister of Scotland for an independence referendum in 2018-19.
"Now is not the time", she said repeatedly in an interview in the Cabinet Room in 10 Downing Street.
She said it would be wrong for there to be a vote until Scots could see the details of the Brexit deal she is about to start negotiating.
And Scottish MSPs needed to be aware of her veto before they vote next week authorising this referendum, less than three years after the first plebiscite.
The prime minister's no risks a serious constitutional crisis.
Because if Scotland goes ahead with the referendum in the absence of a Westminster sanction, it would have the force of popular opinion behind it but not the force of law.