The Liberals have shot down a push by the Nationals to blow up the Murray-Darling Basin plan just two days into Barnaby Joyce’s leadership, and now face demands that the junior Coalition partner be stripped of the water portfolio.

So incensed were the Liberals by what they regarded as an ambush that late on Wednesday, all nine South Australian Liberal MPs and senators, including government Senate leader Simon Birmingham and cabinet minister Anne Ruston, co-signed a stern letter to Scott Morrison.