In a scathing attack on the Labour leader, the Prime Minister ridiculed his statement that he would be "absolutely fine" with a second ballot on breaking up Britain and said Nicola Sturgeon would end up "pulling the strings" .
Joined by Scottish Tory leader Ruth Davidson Mrs May declared she was a "passionate Unionist" and pledged to "fight for Britain" in forthcoming Brexit talks.
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Referring to the London terror attack, Mrs May said the home nations stand together "in this week of all weeks" as "one united people" with shared British values of freedom and democracy.
The reality is, if we lose just six seats, the Government loses its majority
Opinion polls have shown the Tories' UK lead shrinking, sparking speculation of a "vote by vote" arrangement between Labour and the SNP, which could hand the Left-winger the keys to Number 10.
Mr Corbyn last week admitted that he would "open discussions" with the SNP about a second referendum, while Ms Sturgeon has backed a "progressive" alliance to defeat the Conservatives if there is a hung parliament.
Addressing a rally at a home removals firm in Granton, Edinburgh, Mrs May reminded supporters EU divorce talks begin just 11 days after the election.
Theresa May and Ruth Davidson
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She said: "The reality is, if we lose just six seats, the Government loses its majority.
"That would mean Jeremy Corbyn in Number 10 and Nicola Sturgeon pulling the strings from Bute House."
The Prime Minister argued Scots should ask themselves who they trust to stand up for Union, declaring: "Me, I'm a passionate Unionist, I want to ensure the United Kingdom stays together, we strengthen those bonds across the whole of the United Kingdom.
"Or Jeremy Corbyn, negotiating with the SNP for a second referendum, which he is says is 'absolutely fine' by him."
To applause from activists Mrs May added: "I think he's going to find out there is a different view from the Scottish people."
She also urged voters to help her deliver "strong and stable leadership" and rejected Ms Sturgeon's claim that the SNP winning the most Scottish seats would bolster her mandate for a second referendum.
Corbyn last week admitted that he would "open discussions" with the SNP about a second referendum
"We need to pull together in order to try and deliver on the Brexit negotiations, not trying to drive these four nations apart, which is what Nicola Sturgeon is trying to do," Mrs May said.
"In this week of all weeks we stand together, England, Scotland, Wales and Northern Ireland as one United Kingdom."
In a barn-storming speech Ms Davidson told supporters the the “prize” in the election was delivering a firm message to Ms Sturgeon “when she goes back to her desk on Friday” that they do not want another referendum.
She added: "Scottish Conservative MPs aren't going to the House of Commons to try and rip Scotland out of Britain.
"We are there to try and make Britain great again."
Earlier, Ms Sturgeon repeated her her pledge that the SNP would try and prop up a minority Labour government.
Nicola Sturgeon is trying to drive our four nations apart said Theresa May
The First Minister said she thought the Tories would still win but admitted it was "no longer inevitable".
She told BBC Radio Four’s Woman’s Hour: "I’m talking something that would be much more on an issue-by-issue basis to make sure we had government that invested in public services not cut public services, supported pensioner rights, not undermined those rights."
Scottish Labour’s campaign manager James Kelly said Ms Davidson’s pledge to help “make Britain great again” was a “toe-curling” rip-off of Donald Trump’s election slogan.
He added: "The Tories are responsible for Brexit, which was supported by Trump, which handed Nicola Sturgeon a fresh grievance in her bid to break-up Britain."