The group is seeking confirmation from the Inland Revenue that it can arrange a scheme that would stop shareholders being saddled with a tax liability because it is offering them cash, rather than shares.
If the Revenue approves the scheme, Punch will proceed with a bid designed to trump Whitbread's agreed share offer, which currently values the deal at pounds 2.44bn.
City analysts have estimated that Punch might have to pay as much as pounds 3.3bn to trump the Whitbread offer and at the same time compensate for the effects of the tax liability.
Hoare Govett this week said it believes that Punch must offer at least pounds 3.1bn, even if it finds a way to shelter Allied Domecq's shareholders from the tax liability. Other independent analysts say shareholders will prefer Whitbread paper, in order to benefit from synergies worth pounds 100m a year.
Martin Hawkins, an analyst with Greig Middleton, said: "I don't think shareholders will accept cash which is just a fraction above the perceived value of the scheme that can be arranged between Whitbread and Allied."
Observers said it was unlikely that Punch would make an offer substantially in excess of pounds 3bn. Shareholders will vote on the Whitbread deal on 2 July.