The Crown Jeweller is a member of the Royal Household appointed by the British monarch. He or she is responsible for the maintenance and when they leave the Tower of London and security of the regalia and plate which make up the Crown Jewels of the United Kingdom.The Crown Jeweller is a member of the Royal Household appointed by the British monarch. He or she is responsible for the maintenance and when they leave the Tower of London and security of the regalia and plate which make up the Crown Jewels of the United Kingdom.