Taxpayers are facing a bill of up to $20 billion to expand Perth’s shipyard as part of getting it ready to host nuclear-powered submarines and build new warships, in what looms as one of the federal government’s most expensive infrastructure projects.

The AUKUS-related price tag dwarfs the cost of the troubled Snowy Hydro 2.0, which has blown out to $12 billion, and is almost four times the $5.3 billion cost of Western Sydney Airport.