There has been intense speculation that Rupert Murdoch's newspaper publisher intends to extend The Sun to seven days to replace the News of the World, which was shut down in July at the height of the phone hacking scandal.
According to The Guardian, development of the Sun on Sunday was halted in the summer after News International executive chairman James Murdoch said that there were no plans to launch the title.
However, a number of developments appear to demonstrate that the publisher is pushing ahead with the new paper in order to avoid missing out on the lucrative Sunday market.
Staff numbers working at The Sun has increased to around 60, with speculation that former News of the World employees are being lined up to work on the Sun on Sunday.
The Sun also appears to have an excess of editorial chiefs, following the arrival of former Femail and Daily Mail life and style editor Lisa Collins.
Insiders told The Guardian that Collins is being lined up to oversee the Saturday edition of The Sun, replacing former News of the World editor Victoria Newton, who will oversee The Sun on Sunday. Dominic Mohan would edit The Sun from Monday to Friday.
News International is also thought to have hired around 40 new sales staff, suggesting that it is preparing for a big push on advertisers for a return to the Sunday market.
One source told the paper: "It is considered to be an inevitability as far as looking at it commercially; the cost of investment in print plants means they need to have another paper on a Sunday.
"[News International's] commercial side is not in it in a major way yet and I don't expect they will be given a lot of notice, they'll be lucky to come to agencies more than a couple of weeks before launch in my opinion.
"Advance warning to the market would just tip off competitors and give them time to come back on cover price, marketing, promotions or even 'Hackgate' exposés to undermine them."
This Week presenter and former Sunday Times editor Andrew Neil claimed in July that a Sunday edition of The Sun was already being pitched to advertisers by News International.
WPP chief executive Sir Martin Sorrell also expressed his support for a Sun on Sunday title, bemoaning the lack of competition in the Sunday market following the News of the World's closure.
Sources have indicated that the Sun on Sunday will not be introduced until late January or early February, although the launch is still not considered certain.
News International is back in the spotlight today as James Murdoch is due to appear before the Commons culture, media and sport select committee to answer more questions on phone hacking.