'Another two Astutes' is pie-in-the-sky nonsense.
The UK submarine supply chain switched over to Dreadnought a couple of years ago. Dreadnought is needed to replace the aging and increasingly difficult difficult to maintain V boats.
There will be a life extension, technology refresh and capability upgrade for the Collins class unless they decide to buy an interim solution off the shelf (e.g. JB-III or S-80).