Sir Elton John, 76, is among the individuals suing Associated Newspapers Ltd (ANL), publishers of the Daily Mail and Mail on Sunday.
The Your Song hitmaker arrived in a grey suit and was escorted into the courtroom as paparazzi surrounded his car.
Prince Harry and Elton’s husband David Furnish are among those on the list to bring the claim against ANL in October for misuse of private information.
Their lawyers said at that time the group had “become aware of compelling and highly distressing evidence that they have been the victims of abhorrent criminal activity and gross breaches of privacy” by ANL, which is also the publisher of The Mail On Sunday and MailOnline.
In a statement announcing the launch of the legal action, released by Hamlins law firm, it was alleged the unlawful acts included hiring private investigators to secretly place listening devices inside cars and homes and recording private phone conversations.
The list also included “the payment of police officials, the impersonation of individuals to obtain medical information, as well as accessing bank accounts”.