Duchess leaves hospital as radio prank fallout continues

Britain's Prince William stands next to his wife Kate, Duchess of Cambridge, as she leaves the King Edward VII hospital in central London. Photo / AP

Prince William's pregnant wife Catherine has left hospital as a furore continues over a prank phone call made to the private London facility by Australian radio presenters.

The hoax call made by 2Day FM presenters Michelle Greig and Michael Christian to King Edward VII Hospital has sparked international headlines, widespread condemnation, and the threat of legal action.

Pretending to be the Queen and Prince Charles, Greig and Christian called the hospital seeking an update on the condition of Catherine, 30, who was admitted on Monday suffering acute morning sickness.

To their surprise, the pair were connected to a nurse treating Catherine, who referred to Greig as "ma'am" and provided confidential information about the Duchess' condition.

"This is a shocking breach of security," the Queen's former press secretary Dickie Arbiter told British newspaper the Daily Mirror.

"The royal family have been clients of the (hospital) for many, many years and it beggars belief that a member of the public could call up and obtain details of the duchess' medical condition in this way.

"Where on earth were the checks and balances? The hospital will be livid at what has happened and I am sure the palace will be demanding answers."

A spokesman for the hospital labelled the act "foolish" and said advice was being sought about whether legal action should be taken against the broadcaster.

A legal expert told British tabloid The Sun: "It would be open to the attorney-general to consider the possibility of a prosecution for treason."

"To impersonate the monarch is to suggest that you are the monarch and the true monarch doesn't exist," the lawyer said, adding that the offence of treason extends to citizens of commonwealth countries, including Australia.

Greig and Christian have apologised for the prank and sent their best wishes to Catherine.

The call was not the first successful royal hoax.

In 1995, a Canadian DJ spent 14 minutes chatting with the Queen, at times in fluent French, after being connected by the Buckingham Palace switchboard.

Catherine showed no signs of being upset by the prank as she left hospital on Thursday morning (GMT).

Wrapped in an overcoat and scarf and carrying a bunch of yellow flowers, Catherine smiled as she stopped briefly on the hospital steps before entering a waiting Jaguar accompanied by William.

A statement from royal aides said the Duchess would spend coming days resting at her London home, Kensington Palace.

- AAP