SYDNEY EIG Partners CEO Blair Thomas said on Thursday the consortium behind the $10.6 billion bid for Origin Energy was "done" negotiating with top shareholder AustralianSuper in an attempt to gain its backing for the offer.

Thomas said he believed AustralianSuper, which holds 16.5% of Origin, was acting against the best interests of the company's remaining shareholders.

EIG is part of the consortium led by Canada's Brookfield.

(Reporting by Scott Murdoch in Sydney; Editing by Jamie Freed)