The London hospital treating Britain’s Duchess of Cambridge for severe morning sickness admitted it had fallen for a prank call from an Australian radio station.

Kate Middleton was admitted to the King Edward VII Hospital in central London on Monday suffering from Hyperemesis Gravidarum.

Two presenters from the Australian 2Day radio station called the hospital pretending to be Queen Elizabeth and Prince Charles.

Despite putting on unconvincing impressions of the royal duo, they were put through to the ward where Kate is being treated and given intimate details about how she was faring.

"She is sleeping at the moment and she has had an uneventful night," a flustered-sounding nurse told the presenters, who called in the early hours of Tuesday morning.

"Sleep is good for her. She's been given some fluids to rehydrate her because she was quite dehydrated when she came in. But she's stable at the moment."

The nurse tells the pair that they would be welcome to come and visit after 9am when Kate has been "freshened up".

"She hasn't had any retching with me since I've been on duty and she has been sleeping on and off. I think it's difficult sleeping in a strange bed as well."

The hospital confirmed the hoax call had been made and it deeply regretted the incident.

It added that there was no way such a call would have been put through to a patient.

"This was a foolish prank call that we all deplore," John Lofthouse, the hospital's chief executive said in a statement.

"We take patient confidentiality extremely seriously and we are now reviewing our telephone protocols."

Prince William’s office said it would not be commenting on the prank call.

The Sydney radio station that carried out the hoax has issued an apology.

In a statement the station said: "2Day FM sincerely apologises for any inconvenience caused by the enquiry to Kate's hospital.

"The radio segment was done with the best intentions and we wish Kate and her family all the best."