The High Court has bolstered the power of business to define employment by contract, overturning a landmark “double dipping” decision that meant regular casuals were entitled to paid leave and left businesses facing a potential $39 billion backpay bill.

Legal experts said the unanimous ruling handed down on Wednesday was a major precedent on freedom of contract that could have far-reaching implications, including by reducing the scope for sham contracting claims brought against Uber and Deliveroo.