A chainsaw was used on the armoured displayCredit:Nottinghamshire police Their arrests came when officers swooped on properties in the Carlton and Cinderhill areas of Nottingham and the nearby village of Bulwell.Detective Inspector Gayle Hart said: “The stolen property hasn’t been recovered and we still want to hear from anyone who knows where the items might be.“We also want to hear from anyone who has any information about a silver Audi RS5 Quattro, registration number KY61 USJ, which we believe was involved in the burglary. Four suspects have been arrested over the theft of a tiara described as a “national treasure” from a gallery.CCTV showed the moment a gang took a chainsaw to an armoured display case at the Portland Collection in Worksop, Nottinghamshire, on November 20.They snatched the Portland Tiara, a diamond-encrusted gold and silver piece believed to have been worn by the Duchess of Portland at the 1902 coronation of King Edward VII.A diamond brooch was also taken from the display during an audacious raid carried out as alarms were blaring.Nottinghamshire Police said three men, aged 46, 38 and 33, and one woman, aged 30, were being held on suspicion of burglary.None of the stolen jewellery has yet been recovered. “It was stolen from the Phoenix Park Park and Ride tram stop, Millennium Way East, Cinderhill, Nottingham, on Friday 2 November 2018. It was found abandoned and burnt out in Cross Lane, Blidworth, about half-an-hour after the burglary on November 20.”We’re keen to trace this vehicle’s movements before the burglary so encourage anyone who saw it or who has any information to get in touch with us as soon as possible.”Anyone with information is asked to Nottinghamshire Police on 101, quoting incident number 856 of 20 November 2018, or Crimestoppers anonymously on 0800 555 111. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.