In a judgment on Wednesday, the court allowed an appeal by Disorganized Developments Ltd and two of its directors who it identified as members of the gang.

Disorganized Developments is the registered owner of the Cowirra property, about 100 kilometres east of Adelaide.

The state government had previously tried to seize the property as a criminal asset but later dropped that bid.

In 2020 it moved to declare it a prescribed place, meaning members of the Hells Angels, a declared criminal organisation, could not visit.

That move was appealed and lost in the SA Supreme Court but has now been overturned in the High Court.

It found the regulations to be ineffective and therefore invalid, and also that the owners had not been afforded procedural fairness.

“Procedural fairness under this scheme requires reasonable notice to an owner or occupier of a proposal to declare a place a prescribed place,” the court said in its majority ruling.

“To give them an opportunity to supply information or make submissions as to matters within their knowledge as an owner or occupier that may be relevant to a decision to exercise the declaration power.”

The High Court ordered the state government pay the costs of the appeal.