The Duchess of Cornwall applied a traceable liquid called SmartWater to the Royal Artillery Memorial at Hyde Park Corner. The liquid is used to identify memorial plaques that have been stolen.
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The film had formed part of a commemoration to the Choucair family, three generations of whom died in the fire.
John Nolan, who was found with cigarettes and two lighters, suffered burns on 65% of his body after being alight for around six minutes.
Known as Pily she died in January, seven months after the disaster, having suffered a stroke.