It comes on the first day of the prince's legal action against Mirror Group Newspapers (MGN).

In court documents released at the start of the trial, MGN admitted there was "some evidence of the instruction of third parties to engage in other types of UIG (unlawful information gathering) in respect of each of the claimants", of which the Duke of Sussex is one.

The publisher denies involvement in the case of one claimant - Michael Turner.

MGN also said it "warrants compensation".

The publisher added: "MGN unreservedly apologises for all such instances of UIG, and assures the claimants that such conduct will never be repeated".

The statements form part of the publisher's defence to claims brought by Harry and other individuals over alleged unlawful information gathering at MGN titles.

Representing the publisher, Andrew Green KC said in the written arguments that it denied allegations of voicemail interception in the cases being examined during the trial.

Mr Green also said some of the challenges it faces have been brought beyond a legal time limit.

The barrister said: "There is some evidence of the instruction of third parties to engage in other types of UIG in respect of each of the claimants" except for the case of actor Michael Turner whose claim is "entirely denied".

He added: "This apology is not made with the tactical objective of reducing damages, MGN accepts that an apology at this stage will not have that effect, but is made because such conduct should never have occurred."