The extraordinary extent of the illicit surveillance of the young royals by the British tabloids was exposed at the London phone hacking trial today, when a former royal reporter for the News of The World admitted hacking Kate Middleton's phone 'at least' 155 times.

The tireless phone hacker even went so far as to listen to her messages on Christmas Eve, Christmas Day and Boxing Day in 2005, the trial was told.

The paper’s former Royal Editor, Clive Goodman, who has previously been jailed for phone hacking and is a witness in the current trial, also said he had hacked the mobile phone of the Duke of Cambridge on 35 occasions and Prince Harry on nine occasions.

Mr Goodman made the shocking admission as he returned to court following a period of ill health.

He told the court: “There has been no intention to deceive you or anybody else about my involvement in hacking.

“If anyone asks me an open question, I will give an open answer.”

It has long been known that the royals were among the most enthusiastically targeted celebrities by the hackers, and today's revelation that Kate Middleton was hacked so extensively follows evidence last year that a note seized from Mulcaire's premises in 2006 titled "Target evaluation,"had Kate's name on it.

The phone hacking scandal first came to light as a result of royal phone hacking. On November 13, 2006, an article appeared in the News of the World written by Clive Goodman, that claimed that Prince William was in the process of borrowing a portable editing suite from ITV royal correspondent Tom Bradby.

Mr Bradby, a former ITV News royal correspondent, later said of the incident, "I was due to have a private meeting with William and I was pretty surprised to find that, not only details of the meeting but of what we were going to discuss pitched up in the News of the World the Sunday before.

"When he and I hooked up we both looked at each other and said, 'Well how on earth did that get out?' and we worked out that only he and I and two people incredibly close to him had actually known about it.

"

Then we started discussing one or two other things that had happened recently. There had been a meeting he had had with a knee surgeon that again only he and his personal secretary and the knee surgeon had known about that had got into the News of the World.

"

"Basically, the answer we came up with was that it must be something like breaking into mobile answering machine messages."