(CNN) —  

An officer assigned to a unit that protects Britain’s royal household was arrested Thursday on suspicion of unlawfully keeping ammunition in personal lockers in a police building on the grounds of London’s Buckingham Palace, the Metropolitan Police said.

The officer, whom police didn’t name, worked with a Metropolitan Police unit responsible for the royal household’s protection, but he wasn’t assigned to a particular member of the royal family, police said in a written statement.

The ammunition is “believed to be from the Met’s own supplies,” the statement reads.

The officer was in custody and being questioned “on suspicion of misconduct in public office and unlawful possession of ammunition” Thursday afternoon, and his home was being searched, police said.