Caltex Australia has been forced to disclose a beefed-up, all-cash $8.6 billion takeover approach from acquisitive Canadian group Alimentation Couche-Tard after news of the takeover interest leaked into the market.

The petrol and convenience retailer only on Monday revealed a plan to spin off some of its service station sites in an IPO, a move that would derail the takeover ambitions of its suitor, owner of the Circle K brand well known throughout Asia.