Addressing the Conservative party's spring conference, the British PM accused the Scottish First Minister Nicola Sturgeon led Scottish National Party (SNP) of using Brexit as a pretext to engineer divisions within the UK.
"The fact that more Scottish voters backed Scotland staying in the UK in 2014, than supported the UK staying in the EU in 2016 and that almost half a million independence supporters actually backed Brexit last year seems to count for nothing," she said.
"But it would be bad for Scotland, bad for the UK and bad for us all. The coming negotiations with the EU will be vital for everyone in the United Kingdom. Every person, every family, every business, every community the length and breadth of the United Kingdom - England, Scotland, Wales and Northern Ireland," she added.
Reiterating that she will be invoking Article 50 of the Lisbon Treaty to begin Britain's exit from the European Union within the next two weeks, the British PM said she believes Britain's best days "lie ahead".