Petrol and diesel supplier Ampol has lost its second-in-command Louise Warner to its former suitor, Alimentation Couche-Tard, stoking speculation that the Canadian convenience retailer could be gearing up to revive its takeover ambitions.

Ms Warner, a highly experienced fuels industry executive who was overlooked for the chief executive role earlier this year, is understood to have been appointed head of global fuels and trading, based on the US east coast.