Rupert Murdoch's Sun is teetering on the brink of advising its readers of its Scottish edition to vote yes in the independence referendum.

The tabloid has prepared the ground over the past week by damning the Better Together campaign, which is urging the Scots to vote no, and heaping scorn on the leaders of the three main English-based parties.

As the largest-selling paper north of the border, with 246,000 buyers and including many floating voters, the Sun's editorial stance could be influential to the outcome of the vote.

None of its readers can be under any illusion that the Sun has no time for Westminster in general and David Cameron, Ed Miliband and Nick Clegg in particular.

Leading articles over the past three days have condemned the English parties' concessions on greater autonomy for the Scots as "too late" while praising Scotland's first minister, Alex Salmond, for "confidently leading Scotland towards his vision of a promised land".

Twitter followers of Murdoch will also know the media magnate believes "Scottish independence means a huge black eye for the whole political establishment". One of his later tweets was less strident: the people, he conceded, were facing a "hard choice with real pain".

Murdoch's Sun is far from being the only newspaper voice in Scotland, but only one title, the Glasgow-based Sunday Herald, owned by the US group Gannett, has been bold enough to back the yes campaign so far. It announced its decision in May and has had its sales take off ever since, rising by almost 25%, while all the others have lost circulation.

Its editor, Richard Walker, said: "I made the decision because I thought it was the right one, not to win sales. It could have gone either way."

Magnus Llewellin, his opposite number on the group's daily title, the Herald, preferred to play a straight bat, and said he drew heart from the fact that the paper had been attacked by supporters from each side.

The Scotsman in Edinburgh, owned by Johnstone Press, has been more obviously unionist in tone, while the other two big city titles, the Dundee Courier and Aberdeen Press & Journal, have pursued a largely neutral course.

Damian Bates, editor of the Press & Journal, said: "We are simply providing as much info as possible and encouraging readers to make sure they don't miss the opportunity to make their voice heard."

The Daily Record, which sells 204,000 copies a day across Scotland and is a sister title to the Daily Mirror in England, has remain loyal to the Labour party and therefore been generally supportive of the party's anti-independence position. It greeted Gordon Brown's intervention, in which he offered autonomy to Scotland should the no vote succeed, as a "fight to save the union".

At the same time, the Record has been acutely aware of growing hostility towards rule from London. One of its editorials referred sympathetically to "Scotland's genuine disillusionment with Westminster".

More predictably, the Scottish editions of English-based nationals, such as the Daily Express, Daily Star and Daily Mail, have been staunchly unionist.

On Tuesday, the Mail lavished praise on Brown's initiative, urging the people to celebrate "from the rooftops the glorious treasure we share in our British identity". It savaged Salmond in headlines, news stories and an editorial. In a second message the Mail was scathing about the failures of the Better Together campaign in losing a once-commanding poll lead.

Privately, some Scottish editors admit that their influence over the outcome is muted because their readerships are largely drawn from older people who were, in the main, convinced no voters.

One editor said: "We aren't reaching young people because they don't read our papers, and it's pretty obvious that the majority of them are going to vote for independence."