AGL chief executive officer Brett Redman’s shock resignation has thrown Australia’s largest electricity retailer into turmoil, with the chairman forced to step in to manage the company’s looming demerger and find a new CEO.

In early morning trade disappointed investors sent the stock down as much as 4 per cent to lows not seen since 2004 but the shares recovered some ground to close down 2.9 per cent to $8.80.