The high-profile figures, also including Baroness Doreen Lawrence and Sir Elton John, sued Associated Newspapers Limited (ANL) over allegations of unlawful information-gathering.

ANL strongly denied the claims, which were heard at an 11-week trial in London earlier this year, with judge Mr Justice Nicklin dismissing all the cases in a judgment on July 7d

In a judgment on Friday, Mr Justice Nicklin ruled the group of seven must pay £9,544,355 within seven days as an initial contribution to the publisher’s costs ahead of further hearings to determine the total sum.

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He said: “The claimants and their advisers have been on notice, since the hearing, that this would be the date for payment on account.”

Mr Justice Nicklin also ruled that ANL’s costs should be determined on an indemnity basis, which is more favourable to the publisher in terms of the amount it can recover, aside from where orders had already been made.

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He said in the 44-page ruling that he was granting costs on this stricter basis for several reasons, including “the speculative and substantially inferential character of the claims at their origin”, the “exceptional breadth” of the cases “and the public presentation of allegations of serious criminality and impropriety which were not ultimately established”.

He continued that the group are criticised for “the making and maintenance of very serious allegations against many individuals, the failure to reassess those allegations when the evidence required reassessment, and the continued pursuit of allegations which were unsupported or had ceased to be realistically maintainable”.

“In my judgement, that conduct was unreasonable to a high degree,” Mr Justice Nicklin added, later describing the claims as “litigation conceived and pleaded on an unjustifiably wide canvas”.

He also said it was “wholly unacceptable” for lawyers acting on behalf of the high-profile figures to put allegations to witnesses that did not form part of their pleaded cases, which placed the witnesses “in an unfair position”.

An ANL spokesperson said the ruling was “another overwhelming victory for the Mail and its journalism”.

They said: “His judgment is a devastating critique of an attempt to destroy a newspaper and the reputations of its journalists, editors and executives.”

The spokesperson added: “The truth is that these outrageous claims should never have been brought. That they were pursued raises disturbing questions about the conduct of elements of the legal profession.”

Any bids for permission to appeal either the judgment dismissing the cases, or Friday’s ruling, must be filed by October 2.

Friday’s judgment means that the group of household names, which also includes David Furnish, Liz Hurley, Sadie Frost and Sir Simon Hughes, could have to pay millions of pounds out of their own pockets to cover the costs.

The court was previously told there was a shortfall between ANL’s total costs and the group’s insurance cover of a combined £16.2 million.

Nicholas Bacon KC, for Harry and others, said in written submissions that it could be “very significant” if they had to pay ANL’s costs on the stricter indemnity basis and could lead to them being without enough insurance cover, as the publisher’s costs “exceed its approved budget” by more than £18.6 million.

He said that on the standard basis, a judge will need a good reason to award more costs than were set out in court-approved budgets, but this does not apply when costs are awarded on an indemnity basis.

Mr Justice Nicklin described the £34 million costs claim from Associated Newspapers Limited as “excessive” and “largely unexplained” but declined to impose a cost cap after “careful consideration”.

If the two sides cannot agree the total amount that should be paid, further hearings in front of a specialist costs judge will take place.

Mr Justice Nicklin added: “Indemnity assessment is not a blank cheque. Associated itself accepts that even on an indemnity assessment the costs judge must consider whether the costs were reasonably incurred and reasonable in amount.”

Sir Simon said he was “disappointed and surprised” that ANL’s recoverable costs had not been limited.

He added: “I am now taking the time necessary to consider both the substantive and the costs judgment and whether to pursue appeals against decisions in either judgment or both.”

David Bailey-Vella, chairman of the Association of Costs Lawyers, said that without a settlement the costs process “will not be quick” and could take several years.

He said: “This could not have gone much worse for Prince Harry and the other claimants.

“An award of costs on the indemnity basis disapplies the court-approved costs budget – which is vital for Associated as it spent much more than it said it would – and removes the requirement that the costs must be ‘proportionate’. They must still meet the test of being reasonably incurred and reasonable in amount, however.”

The judgment comes after it was made public on Wednesday that Harry and his wife the Duchess of Sussex are moving back to the UK.

The couple decamped to California more than six years ago amid the Megxit crisis, but will relocate back to the UK later this month to live in a non-royal residence outside London.

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