Queensland is working on a secret deal to buy a 50 per cent stake in one of the state’s biggest coal-fired power plants, Callide C, but its plan must survive a legal challenge brought by a Czech billionaire’s family office.

Queensland’s CS Energy, a government-owned energy corporation, is seeking to pay about $230 million for the 50 per cent stake, including $67 million cash, waiving debts worth more than $160 million.