At the meeting earlier this week Nomura is believed to have told Offer that it would inject a substantial chunk of its own cash into a new company created to buy Energy Group, scotching fears that the vehicle would carry an excessive debt burden.
Industry sources said the bank had emphasised that its bid would result in less debt for Energy Group, which owns Eastern Electricity, than with the pounds 4.06bn offer launched by PacifiCorp of the US on Tuesday.
Nomura's emerging bid plans are thought to involve the company injecting at least $2bn (pounds 1.3bn) of equity into the group.
Last week Nomura revealed it would split up Energy Group and ultimately return Eastern Electricity to the stock market as a separate company, a move which is expected to please the industry regulator.
PacifiCorp was cleared to bid for Energy Group by the Monopolies and Mergers Commission last December, but has argued that ruling was specific to the Oregon-based utility and did not mean other rival bids had also been given the green light.
The new bid would leave PacifiCorp with almost pounds 10bn of debt.