The Met’s decision to refer itself to the IOPC was described as voluntary, reflecting the seriousness with which the force views its earlier handling of the matter.
It remains to be seen what action, if any, the police watchdog or foreign agencies may take in response.
Last week, a Met Police spokesman said: “Following a thorough review of Met Police systems and records, we have confirmed that in January 2019, we received a letter containing a number of claims about alleged offending outside the United Kingdom. It was sent to the MPS Protection Command to raise concerns in relation to the security of the Duchess of Sussex.
“The letter was reviewed and a decision was made that it should be passed to the office of the Duke and Duchess of Sussex for their awareness. The details of the allegations in the letter were not shared with other law enforcement agencies.
“The MPS is reviewing the handling of this matter in 2019 and considering whether a referral to the IOPC is necessary to review our approach.”