Prince Harry and six other high-profile figures will have to make an initial payment of £9.5 million (A$18 million) toward the legal costs of a British tabloid publisher after losing a high-stakes case against them last month, a UK High Court judge ruled Friday.

The group – which also included Elton John and his husband, David Furnish – lost a case against the publisher of the Daily Mail over allegations of unlawful information gathering for stories published between 1997 and 2015.

This figure, which must be paid to Associated Newspapers Limited (ANL) by 4pm BST (1am AEST) on August 28, is only an initial sum and not the full total the group will eventually pay, the court said in its ruling.

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Unusually, the ruling does not require the publisher to prove that its claim for costs is reasonable; instead, it will fall to the claimants to argue their case if they believe it is not.

Prince Harry faces a mammoth bill for the Daily Mail's legal costs following his loss in court. (EPA PHOTO) Credit: AAP

Explaining the reasons for this, the court was highly critical of the claimants’ case, saying it had been made “outside the ordinary and reasonable conduct of civil proceedings.”

However, this is “not a blank check” for ANL, who cannot recover “unreasonable” costs, the court added. In July, the publisher initially estimated its legal costs to be £34.5 million (A$65 million), which the court said was “exceptionally high.”

Still, the court declined to impose a cap on the costs ANL could claim, saying that a more detailed assessment process involving a specialist judge could better settle any dispute.