The High Court has cleared the way for a Sydney radio station to face serious penalties over a prank call to a London hospital in which two presenters posed as the Queen and Prince Charles.

DJs Mel Greig and Michael Christian from 2Day FM rang the hospital treating the Duchess of Cambridge for morning sickness in December 2012, pretending to be the Queen and Prince Charles.

Nurse Jacintha Saldhana, 46, passed the call through to the ward and, following a storm of publicity about the fact the presenters had obtained personal details about the Duchess, she later took her own life.

A UK inquest into her death was later told she blamed herself for the incident.

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The Australian Communications and Media Authority (ACMA) ruled the station had breached the law by broadcasting the call without the consent of the other party.

It considered the station had breached New South Wales surveillance laws with the prank call.

The radio station then successfully took legal action against the ACMA in the Federal Court, which found the authority had no power to determine matters of a criminal nature.

Jacintha Saldanha, took her own life following the prank phone call in 2012. ( ABC TV )

But this morning the High Court overturned that decision, finding the media watchdog did have the power to rule if a criminal offence had been committed.

It found the ACMA did have power to make an "administrative determination" that the station had committed a criminal offence, as a preliminary to taking enforcement action under the Broadcasting Services Act.

The court found that in making the determination, the authority was not exercising judicial power.

Mr Christian and Ms Greig both apologised for their actions in the wake of the scandal, saying they were devastated by Ms Saldanha's death.

Ms Greig also voluntarily flew from Australia to London to attend the inquest into the nurse's death, making a statement to the court and apologising personally to Ms Saldanha's family.

Following today's decision Southern Cross Austereo (SCA), the owner of 2Day FM, issued a statement that said it was "important to note that the case dealt only with the power of the ACMA under the Broadcasting Services Act and did not consider or make any findings about the conduct of SCA or 2Day FM".

"SCA was informed by the NSW State Police and the Australian Federal Police late last week that they have completed their investigations of the recording of the prank call by 2Day FM and have concluded that the recording of the prank call by 2Day FM did not breach the NSW Surveillance Devices Act, the Commonwealth Telecommunications Interception Act, or any other law."

SCA said the court's decision meant there was a serious defect in Australian broadcasting law and it would seek to have the law changed "as a matter of urgency".

Free TV Australia and Commercial Radio Australia (CRA) have also expressed concern over the High Court ruling.

CRA chief executive Joan Warner said in a statement: "It means that the ACMA can now act as police, judge and jury."