Ministers believe Boris Johnson could have no choice but to grant permission for a second Scottish independence vote if Nicola Sturgeon and Alex Salmond win two thirds of seats at the Holyrood election next month.
Mr Johnson has repeatedly said he will not give the green light to a re-run of the 2014 referendum, insisting that vote was a once in a generation event.
But some senior figures in Westminster believe the PM will have to change tack if the SNP and Alba Party win enough seats for a pro-independence supermajority of MSPs.
There is also a belief held by some in Whitehall that it would be better to hold a second vote sooner rather than later so that the benefits of the Union to the recovery from the Covid crisis can be stressed.
Boris Johnson has repeatedly said he will not give the green light to a re-run of the 2014 referendum, insisting that vote was a once in a generation event
But some senior figures in Westminster believe the PM will have to change tack if the SNP and Alba Party win enough seats for a pro-independence supermajority of MSPs
Sources told The Sunday Times that Mr Johnson is publicly and privately '100 per cent against' a referendum.
But some ministers believe Mr Johnson could be forced to grant permission for a second vote, depending on the outcome of the Holyrood election.
One senior minister told the newspaper: 'I don't see how we keep saying 'no' forever.
'The time to do it would be in the middle of economic chaos, not when it's all looking rosy.'
A senior Tory said: 'Boris said a lot about honouring democratic votes after the EU referendum. If Scots vote for a referendum, ultimately they'll have to have one.'
It came as a new survey conducted by Panelbase revealed that 46 per cent of voters believe there should be a referendum if pro-independence parties secure a supermajority while 38 per cent disagreed.
Some 36 per cent of respondents said they would back a unilateral declaration of independence in those circumstances.
A Savanta ComRes poll published last week suggested that the Alba Party could actually ruin Ms Sturgeon's hopes of winning an outright SNP majority.
It predicted the SNP could return 64 MSPs, one short of the 65 needed for a majority.
The poll suggested the Alba Party could return none - meaning no Holyrood return for Mr Salmond himself - but it is forecast to take three per cent of the list vote, which would be enough to derail Ms Sturgeon's hopes of governing alone.