New Zealand's top judge will preside over a mock trial marking the 800th anniversary of Magna Carta in London later this month.

Chief Justice Dame Sian Elias, the most senior judge in New Zealand, will sit alongside Lord Neuberger, president of the UK's Supreme Court and Justice Stephen Breyer of the US Supreme Court, to sit in judgment of the barons and bishops who on June 15, 1215 forced King John to sign Magna Carta, which helped lay the foundations of the British state based on the rule of law, fair and swift trials and property rights.

The mock trial, staged on July 31 at Westminster Hall in London, will see the barons and bishops tried for treason.

"Judges never usually comment before a case but in this instance, I think I can safely make an exception," Lord Neuberger told the Guardian.

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"We will be deciding whether, setting aside the global impact of some of the ideas embedded in Magna Carta, the barons' actions in 1215 could be justified in law.

"We can't promise a polished theatrical performance, but we do hope to offer a creative and interesting way of retelling the great Magna Carta story that encourages people to think about the battle of wills and principles that lay behind this world famous treaty."

English comedy writer Clive Anderson will play a leading role along with advocates from across the Commonwealth who will make the cases for the prosecution and the defence.

The Guardian reports that the "verdict" will be published on the UK's Supreme Court website at https://www.supremecourt.uk/