The stresses of touring New Zealand in 1981 – shortly before his wedding to Lady Diana Spencer – weighed heavily on England’s future King, it has been revealed.

Prince Charles wrote to friends at the time that if “one more New Zealand child asks me what it’s like to be a prince, I shall go demented”, Britain’s Guardian newspaper reported.

The heir to the throne added: “Will you visit me when they strap me in a white apron and deposit me in some institution? I am beginning to get fed up with the amount of nonsensical rubbish I take all day and every day.”

His comments come on the eve of younger sister Princess Anne’s arrival in New Zealand tomorrow to represent her father at the 23rd Commonwealth Agricultural Conference.

She will present the award for the Royal Agricultural Society supreme champion animal tomorrow and on Saturday will present the New Zealand Cup at the Riccarton race meeting.

In a BBC fly-on-the-wall documentary screened last night in Britain to mark his 60th birthday, Prince Charles was asked if he enjoyed the job.

He replied: “I don’t know. Well, there’s bits of it.”

The Telegraph newspaper reported that the Prince continued: “It is something that I feel I must do – to help as many other people as I possibly can in this country.”

During the fly-on-the-wall film he talked about his hopes that Prince William and Prince Harry would maintain his legacy by continuing his charitable work when he becomes King.

He also lavished praise on the Queen for her commitment to her public duty.