The King was too "busy" to meet with his son after the Duke of Sussex made a surprise visit to London to attend a High Court hacking case against a newspaper publisher.

The Duke of Sussex attended the hearing to throw his weight behind a legal claim against Associated Newspapers Limited (ANL), the publisher of the Daily Mail, over alleged phone hacking and misuse of private information.  

Prince Harry flew commercial from California to London for the four-day preliminary hearing because he wanted to show his support, the Telegraph understands.

But he is not expected to see his father during his visit, despite making contact, because he was told he was busy.

The King is understood to be at Highgrove, in Gloucestershire, and neither the Prince and Princess of Wales nor their children are in London or Windsor because it is the school holidays, palace sources said. 

The hearing was due to coincide with the King’s state visit to France before the trip was cancelled on Friday because of ongoing civil unrest and violence over Emmanuel Macron’s pension reforms. 

The Duke’s presence in court will undoubtedly draw attention to the case and may have overshadowed the visit had it gone ahead. Arriving with a small team of staff on Monday morning, he smiled at the press and bumped into a photographer as he walked into the building shortly before 10.30am. 

He sat in the body of the court alongside his lawyers, wearing a navy suit and tie. As the hearing got under way, he leant forward on the desk with his hands clasped, listening intently.

Court proceedings began with a bid by ANL’s lawyers to have certain reporting restrictions imposed in the case. The Duke occasionally took notes in a small black notebook as legal arguments were made by Catrin Evans KC, ANL’s barrister.

Sadie Frost, the actress who is also bringing a claim against the publisher, sat two seats away from Prince Harry.

The Duke is among seven high profile figures suing Associated Newspapers Limited (ANL). The other claimants are actress Elizabeth Hurley and Ms Frost, the singer Sir Elton John and his husband David Furnish, Baroness Doreen Lawrence and the former Lib Dem MP Sir Simon Hughes.

In a joint statement released in October, the group said they had become aware of “compelling and highly distressing evidence that they have been the victims of abhorrent criminal activity and gross breaches of privacy”.

The publisher strenuously denies the allegations. It has described them as “preposterous smears” and a “pre-planned and orchestrated attempt to drag the Mail titles into the phone-hacking scandal”.

The preliminary hearing scheduled for this week will allow Mr Justice Nicklin to determine whether the case can continue. The judge will hear legal arguments relating to an application by Associated which alleges, among other things, that the claimants’ use of information is in breach of a restriction order made by Lord Justice Leveson.

The claimants are all represented by David Sherborne, a barrister who had access to the information as a representative of core participants at the inquiry 11 years ago.

Associated is expected to argue that no application was made to use that information and that therefore any claims based upon it should be struck out.

ANL has also made an application, which has not been opposed, to anonymise journalists named until the judge has decided whether or not the claims should proceed. Full details of the claims have not yet been revealed and will remain sealed until the issue has been resolved.

However, the claimants allege that Associated, the publisher of the Daily Mail, the Mail on Sunday and MailOnline, hired private investigators to put listening devices in their homes and cars, that people were paid to listen in on live telephone calls and record them and that bank accounts and other financial information were “accessed through illicit means and manipulation”.

They are also expected to argue that police officers with links to private investigators were paid for private information and that individuals were impersonated to obtain medical information from private hospitals, clinics and treatment centres by deception.