Rosie Henderson invoked the clameur by kneeling and crying for help and reciting the Lord’s Prayer, in Norman French.

The act is fully enforceable in the law of Guernsey and Jersey and it means that construction in St Peter Port must cease until a court deals with the case, The Guardian reports.

Henderson invoked the ancient law yesterday by Les Échelons and South Esplanade, which lie near the construction site.

The clameur states: “Haro! Haro! Haro! A l’aide, mon prince, on me fait tort”, which in English is “Come to my aid, my prince, for someone does me wrong”.

She has 24 hours to register the clameur in court.

According to legend, the clameur originates in the early Norman period and is believed to have been a plea to Rollo, first Duke of Normandy.