How was the worlds largest diamond shipped to England in 1905?

According to the citation in Wikipedia, below:

"In 1905, transport from South Africa to England posed a security problem. Detectives from London were placed on a steamboat that was rumoured to carry the stone, but this was a diversionary tactic. The stone on that ship was a fake, meant to attract those who would be interested in stealing it. The actual diamond was sent to England in a plain box via parcel post, albeit registered."