A major proxy adviser with significant sway over Origin Energy investors has recommended they back a near-$20 billion takeover proposal for the electricity and gas giant despite describing it as an “uphill battle” given opposition from the company’s largest shareholder.

CGI Glass Lewis said there was “sufficient evidence” to support Origin’s view that the offer from the North American suitors was “attractive” adjusted for the risks involved with the energy transition. The takeover is opposed by AustralianSuper, which controls 15 per cent of the register.