The Metropolitan Police has referred itself to the Information Commissioner's Office after the names of the alleged victims of the Westminster honeytrap scandal were revealed to each other.
The force has apologised "sincerely for any distress" after an email was "sent in error".
According to reports, the Met sent an email to all those thought to be victims of the scandal - but instead of the email addresses of the recipients being hidden, they were visible to each other.
Officers will be reminded that care should be taken when sending group emails, Sky News understands.
The email is understood to have been a short, routine update to the investigation.
A Met Police spokesperson said: "An email relating to an ongoing investigation was sent in error today.
"We recognise the impact on those involved and apologise sincerely for any distress.
"A referral to the Information Commissioner's Office has been made and we await advice on next steps.
"Officers will be reaching out to those impacted to personally apologise and provide reassurance."
The honeytrap scandal was a sexting scam in which at least 12 men in political circles received unsolicited, flirtatious WhatsApp messages from people calling themselves "Charlie" or "Abi".
Explicit images were exchanged in some instances.
Former Tory MP William Wragg resigned the whip after he admitted giving out fellow politicians' phone numbers to the suspected perpetrator.
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Another MP targeted - the Conservative's Dr Luke Evans - confirmed the incident.
He said: "As someone who has spoken publicly about the impact of being targeted, I will be looking to raise this serious matter further."
The ICO said: "The Metropolitan Police have made us aware of an incident and we will assess the information provided.
The watchdog added: "People have the right to expect that organisations will handle their personal information securely and responsibly.
"If an individual has concerns about how their data has been handled, they should raise it with the organisation, then report them to us if they are not satisfied with the response."
Parliamentary authorities have also been updated on the incident.
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In June, a man was arrested as part of the investigation into the scandal.
The Metropolitan Police said they arrested a man in his mid-20s in Islington, north London on suspicion of harassment and offences under the Online Safety Act.
Sky News understands that he was a member of the Labour Party, but has since been suspended.
(c) Sky News 2024: Met Police refers itself to information watchdog after Westminster hone