Cloud over rivals when Sun comes out on Sunday?

Then again, it isn't really new. It will simply be a seventh-day incarnation of the Sun rather than a separate Sun on Sunday, which also enables it to avoid the unfortunate acronym SoS.

In a sense, it can be seen as a rescue operation to answer a mayday call. Murdoch was facing a mutiny among Sun journalists, who were extremely upset at the arrests of 10 colleagues. The launch is an astute way to turn negative feelings into positive ones among a demoralised staff.

They may feel differently when they realise how much extra work is involved down the line, along with amended rotas and so on. For the moment, however, they have been placated by an initiative that assuages their deepest fears about Murdoch turning his back on them altogether.

By contrast, the publishers and editors of the trio of competing red-top Sunday titles - the Sunday Mirror, the People and the Daily Star Sunday - will surely be feeling very differently.

Since the closure of the News of the World last July, they have enjoyed bumper sales lifts, reversing years of decline. Now they must face a circulation war against the world's shrewdest newspaper magnate with an unprecedented track record in risking all to turn potential defeat into victory.

Trinity Mirror, in particular, is about to face a stern test. Chief executive Sly Bailey has always eschewed a price-cutting strategy. She has also pruned promotional budgets to a minimum. And she has just reduced overall editorial staffing by more than 18%, a cost-cutting exercise that has
not been received well on the newsroom floors.

Now she faces the likelihood of thousands of Sunday Mirror and People buyers taking their money back to Wapping by electing to read the new Sabbatarian Sun. There can be little doubt that Murdoch will spend, spend, spend to win back as many of his old News of the World audience as possible. He is on a personal mission to regain public respect after months in which his name has been dragged through the mire.

Murdoch and Bailey also happen to share a similar problem: sceptical investors. Murdoch's US shareholders care little for a troublesome British outpost that produces so little for News Corp. As for Bailey, Trinity Mirror's shareholders have become increasingly concerned about the lack of a dividend, faltering profitability and, at a personal level, the disconnect between her handsome financial reward and the company's ugly performance.

The difference is that Murdoch has more control over his fate than Bailey. Though his company may be under intense scrutiny, with ongoing legal investigations and liabilities that could cost many millions of pounds, he is still a master of the newsprint business.

So what are the prospects for his inky new baby? One plus is that the Sun brand has not been tarnished by what happened to its now-defunct sister, nor by the arrests of its own journalists (none of whom have been charged).

So there is a chance that its sales, running at an average across six days of 2.75 million, could be matched on a Sunday.

If that were to happen, all the gains enjoyed by the rival trio would vanish and they would resume their previous decline. However, that decline was also afflicting the News of the World, and all Sunday titles for that matter. The market itself is disappearing.

People who try the Sun next Sunday will also realise that it is not the News of the World reborn. The sleaze element - the intrusive and sordid kiss-and-tells, for example - will not be there. Page 3 will not feature a topless model. We can expect instead a breezier Sun-alike formula, with the accent on celebrity, sport and those kinds of offbeat news stories that enable sub-editors to write memorable headlines. It will also have the benefit of a glossy magazine, Fabulous.

Early hints suggest there will be investigative articles too. I suppose it's remotely possible that the NotW's former investigations editor, Mazher Mahmood, could switch from the Sunday Times, where he has made almost no impact. If so, he might become the fake sheikh all over again.

Can it succeed? In the current market, if, after six weeks, it is selling more than two million - and therefore heading the Sunday sales chart again - then it will surely be judged a success irrespective of its cover pricing and the enormous promotion spend.

Roy Greenslade is Professor of Journalism, City University London and writes a blog for the Guardian