According to the Financial Times, Blackstone has joined the mass of companies jostling for a hold on the maker of the Jaffa Cakes and KP Nuts brands.
Blackstone's main competitor for the takeover is a consortium led by Premier Foods who are in talks with private equity firm Lion Capital.
However the paper suggests that lack of funds will severely hinder Premier's bid if talks with Lion fail.
With the UB bid, Premier is seeking to add to an already substantial portfolio - in July, the company gained its sixth acquisition in under four years with the £450m (€665.6m) takeover of Campbell Food's Irish and UK businesses.
Both Premier, who own the Branston and Ambrosia brands, and Blackstone, who last year took over Cadbury Schweppes' European drinks businesses, are vying for UB's lucrative northern European sector.
In July City analysts predicted that UB businesses in that area, which include three of the top five biscuits brands in the UK, were worth £2.3bn (€3.4bn).
The Premier-led group include Dutch firm NPD Capital which owns Continental Bakeries and, if victorious in the auction, is rumoured to be taking over UB's Northern continental European businesses.
Following a strategic review of the company undertaken by Goldman Sachs earlier this year, UB opted to sell its southern European business to US giant Kraft, who already owned a 25 per cent share in the food group, for £575m (€850.7m) - giving the snack company seven of the top ten best selling biscuits in Spain.
UB currently own a quarter of the British biscuit industry and in April announced a year-end profit jump to £204m (€301.7m) - up from 2004's £163m (€241m).
Analysts predict sales at the group to rise five per cent in the pre-June period and an increase of 20 per cent in business profit.