It is understood that Paribas has teamed up with Germany's Deutsche Bank and the UK's Cinven Group to prepare an offer of about pounds 1.2bn, or 245p a share, for the maker of Hula Hoops crisps and McVitie's biscuits.
The terms of the deal are said to include a sale of some of UB's assets to Danone, the world's biggest biscuit and dairy products maker.
Analysts say the US companies Hicks, Muse, Tate & Furst, Keebler Foods and Nabisco Holdings, are all still in the running to buy UB and could launch a counter-bid once Paribas makes a formal takeover approach.
UB effectively put itself for auction in October, when it announced it was in talks with various parties. The shares, which yesterday closed down 3p at 227p, have risen about 20 per cent since 3 October, the day before the announcement.