Twelve men and a woman have appeared in court charged in connection with the theft of a £3.5 million Cartier tiara worn to the coronation of Edward VII.

The Portland Tiara, described as a “national treasure”, was stolen during a break-in at an art gallery on the Welbeck Estate in Sherwood Forest in November 2018, Nottinghamshire Police said.

A diamond brooch, which had been alongside the tiara inside an armoured glass display case, was also taken during the burglary at Harley Gallery in Worksop, Nottinghamshire.

On Thursday 13 people aged between 21 and 49, all from Nottinghamshire, London and Birmingham, appeared at Nottingham Magistrates’ Court charged with various offences in connection with the alleged conspiracy.

The police said the defendants had been bailed conditionally to appear at Nottingham Crown Court on November 19.

The 6th Duke of Portland commissioned Cartier to create the Portland Tiara for his wife, Winifred, Duchess of Portland.

She wore the diamond-encrusted headpiece, whose centrepiece is the Portland Diamond, to the coronation of King Edward, the Queen’s great-grandfather in 1902.