Jim Spowart, the founder of Intelligent Finance who is fronting a mystery bid for HBOS, has said he will put up or shut up on any offer this week.
Mr Spowart is hoping to spoil LloydsTSB's £6.5bn purchase of HBOS, which was given the Government's blessing at the end of last month.
He said: "Negotiations about a possible bid are still ongoing. We expect to be able to make a statement either way this week. I have to be careful what I say, given Takeover Panel rules."
Last week Mr Spowart, who left HBOS in 2003, was rapped over the knuckles by the panel, which regulates mergers and acquisitions, after news of a possible bid was leaked to the media following talks with the Scottish Secretary, Jim Murphy.
"It was important to speak with Jim Murphy to make sure the door was open," said Mr Spowart. "We haven't spoken since."
Mr Spowart added that he was "going away for the weekend to get away from the madness".
The City has, so far, remained sceptical about the seriousness of any Spowart offer, which is being advised upon by the little-know European American Capital, an investment house run by Tim Goode, the former treasurer of the Royal Bank of Scotland and chief executive of Halifax's Capital Markets division. Mr Spowart has, so far, only said the suitor is a "foreign bank", refusing to give more details.
LloydsTSB chairman, Sir Victor Blank last week dismissed Mr Spowart, saying that he "wasn't losing any sleep" over the prospect of a rival offer: "There are very few institutions with the capital strength and funding to do the deal."
Sources close to the Treasury said that while it would scrutinise any rival bid, it remained dubious that a serious bid would emerge.