The strategy document was leaked to Bloomberg and suggests handing more powers to Holyrood and putting a new agreement to a popular vote to stave off another referendum.
Speaking today, the PM’s spokesman claimed he had not seen the memo, and the UK Government was focusing on dealing with coronavirus.
He said: “The issue of independence was settled when the Scottish people voted decisively to remain part of a strong United Kingdom.
“Both sides committed very clearly to respecting the decision in 2014 and the First Minister promised it would be a once-in-a-generation vote and the UK Government will continue to uphold that decisive decision.
“What we're focused on is a strong UK-wide response to coronavirus and ensuring that all parts of the UK can build back better in response.”
It comes as the latest poll put support for Scottish independence at 58 per cent, showing the scale of the challenge facing Mr Johnson.
The new 21-page memo analyses polling trends, voter intentions, and comes up with strategies to stop another vote.
It warns: “If the SNP builds on this momentum, then the end point could be a full-blown constitutional crisis or a second independence referendum.
“Either of these outcomes would consume significant political capital for the government.”
The document also warned Brexit has had a monumental impact on support for independence, and suggests “co-opting the EU into demonstrating that there is no viable pathway to renewed membership”.
It explains: “Put simply, there are not enough Leave voters to convert to the ‘No’ side to make up for the movement of Remain voters into the ‘Yes’ camp.
“Another option set out in the memo would be to prepare a new constitutional plan ready to roll out in case of an SNP victory in May.
“These measures could eventually be ratified via a referendum as a ‘placation’ against the SNP’s demands for an independence vote.”
The memo was written by the Hanbury consultancy and looks at what the UK Government should do if the SNP secure another victory.
It is believed to have been circulated by a small group of people, including Tory Cabinet minister Michael Gove.
The SNP claimed the memo showed Westminster was terrified of another referendum.
Deputy Westminster leader Kirsten Oswald MP said: “This leaked memo reveals that the Tories are in panic mode because people in Scotland know Boris Johnson’s government can’t be trusted to act in Scotland’s interests.
“The Tory attempt to deny the right of the people of Scotland to decide their own future is completely unsustainable and undemocratic.”
Scottish Greens co-leader Patrick Harvie accused the UK Government of being in panic mode.
He said: “The idea the Tories could successfully ‘co-opt’ the EU into anything is laughable given they have approached Brexit negotiations in the spirit of a toddler having a tantrum.
“I don’t see any chance that voters in Scotland would be hoodwinked by Trojan horse solutions from a Government that has broken promises on devolution, dragged Scotland out of Europe and is in the process of giving itself a veto over Scotland’s democracy.”