In a front page that riffed on the arrival of the royal baby, Britain's biggest-selling paper put "It's a Tory" as its headline above an image of Cameron swaddled in a blanket.
"It's the Tories. The Tories who rebuilt the economy wrecked by Labour -- and transformed lives. The Tories who alone are committed to an EU referendum," the front page read.
It went on: "The Tories who alone can prevent a nightmarish Labour Government, propped up by the saboteurs of the SNP."
"We believe the Nats will fight harder for Scotland's interests at Westminster, offering a new hope for our country," the front page of the Scottish Sun read.
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The eye-catching front page showed SNP leader Nicola Sturgeon as Princess Leia in "Star Wars", with the headline "Stur Wars: a new hope".
A spokesman for The Sun said "The Sun is written first and foremost for its readers, and the UK edition and Scottish edition have two very distinct audiences."
"If Scotland and England were playing each other at football, no one would expect The Scottish Sun to support the English national team."
The Sun backed the Labour party for ten years under Tony Blair, but switched to the Conservatives in 2010.