Tony Carty, professor of public law at the University of Aberdeen and Cheng Yu Tung Chair of Public International Law at Tsinghua University Law Faculty

Manipulation of opinion by the United States and its allies lies behind the arbitration being sought unilaterally by the Philippines against China on South China Sea issues, according to a British legal expert.

Tony Carty, professor of public law at the University of Aberdeen and Cheng Yu Tung Chair of Public International Law at Tsinghua University Law Faculty, spoke with the arbitration tribunal expected to deliver a ruling soon.

Carty said China should have a "clear strategy" and embark on "a massive and very effective international publicity campaign to show that the tribunal has been biased in its judgment about jurisdiction".

In the likely event of an unfavorable final judgment against China, Beijing must get its message across effectively to world opinion on why it disagrees with the tribunal's decision, Carty said.

China has refused to be any part of the arbitration since the proceedings were launched in 2013 under the United Nations Convention on the Law of the Sea.

This month, Carty was among an international group of legal experts and lawyers who signed a legal opinion document questioning the tribunal's jurisdiction.

Carty spoke of concerns about "a one sided interpretation of ambiguous terms the Convention" from the potential ruling of the Tribunal.

The interpretation may break the archipelago of the Nansha Islands into so-called individual geographical features, he said.

Carty added that some politicians in the US and Britain, as well as some media outlets, had said that the tribunal is permanent and "some kind of final court of appeal".

"But in fact it is merely arbitration, in which one of the parties is not prepared to participate."

Cambodian Prime Minister Hun Sen said on Monday that the forthcoming ruling will be "politically motivated" and Cambodia will not support it.

The tribunal is a special one set under the Convention, and although it is registered at the Permanent Court of Arbitration in the Hague, the court has no particular authority because it depends entirely on consensual proceedings, Carty said.

He said the US has had a South China Sea strategy since 1945. "From its point of view, the security consideration is the primary one," he said.

If the ruling is made, it is likely that "the US and other defenders of the rule of law will come rushing to defend the Philippines" and to ensure that China does not enforce any of its claims, Carty said.