The eyes of the media will return to the High Court in London as the Duke of Sussex is set to find out whether his legal action against the publisher of the Mirror has been successful.

Harry entered the witness box in a trial over contested allegations of unlawful information-gathering by Mirror Group Newspapers (MGN).

With the judgment in the case due on Friday, the PA news agency looks at why the duke came to court and what the case is all about:

– What is the legal action against MGN?

The duke and other high-profile individuals are suing the publisher of the Daily Mirror, the Sunday Mirror and Sunday People.

They are seeking compensation over allegations MGN was involved in the unlawful gathering of their personal information for stories.

Duke of SussexThe Duke of Sussex at the Royal Courts of Justice (James Manning/PA)

Claims brought by four individuals, including the duke, were heard in a civil trial as “representative” cases of the types of allegations facing the publisher, findings over which could affect the outcome of other claims.

– What is unlawful information gathering?

It has been alleged that MGN’s journalists were linked to voicemail interception, colloquially known as phone hacking, securing information through deception and hiring private investigators for unlawful activities.

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Lawyers for Harry, whose case covers the period 1995 to 2011, told the trial that such practices were “habitual and widespread” amid a “flood of illegality”.

– What has MGN said in its defence?

MGN is largely contesting the claims brought against it, but has offered Harry an apology for an instance of unlawful information-gathering.

The publisher said it was admitted that a private investigator was instructed by an MGN journalist at The People to gather information about his activities at the Chinawhite nightclub one night in February 2004.

MGN says board members have denied knowledge of unlawful information-gathering activities and claims there is “no evidence, or no sufficient evidence, of voicemail interception” in any of the four claims chosen as representative cases – some of which it claims are brought too late.

– Who else is involved in the case?

Former Coronation Street actress Nikki Sanderson, comedian Paul Whitehouse’s ex-wife Fiona Wightman and Coronation Street actor Michael Turner – known professionally as Michael Le Vell – also had their claims considered as “test cases” at a trial.

MGN phone hacking trialMichael Le Vell arrives at court (Jordan Pettitt/PA)

All three also gave evidence.

– Has the duke been to the High Court before?

Yes. In March, Harry made a surprise appearance at the Royal Courts of Justice in London amid a preliminary hearing in a similar case he is bringing against Associated Newspapers Limited (ANL), publisher of the Daily Mail.

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The duke is also suing News Group Newspapers (NGN), publisher of The Sun, over alleged unlawful information-gathering, and is bringing a legal challenge against the Home Office in relation to his security arrangements in the UK.