A local Labour Party branch is being investigated by the Metropolitan Police over allegations of "computer misuse" in their selection process.
The new constituency of Croydon East, created after boundary changes ahead of the next election, was paused last year following complaints to party chiefs.
There were suggestions that some of the data held about local members was inaccurate.
This week, the Met Police confirmed a criminal investigation has been launched as a result of allegations of "computer misuse". This came after the party held its own independent inquiry.
A local Labour Party branch is being investigated by the Metropolitan Police over allegations of "computer misuse" in their selection process
PA
A spokesperson for the force said: "We have received allegations of computer misuse in relation to an internal selection process for a political party in Croydon during October and November last year.
"The Met’s cyber crime team are investigating and enquiries are ongoing."
It is illegal to access a computer or change files on a computer without permission under the Computer Misuse Act.
In November, regional Labour bosses sent an email, seen by website LabourList, saying that candidate selection in Croydon East had been suspended "as a result of complaints received by the party that require investigation".
They said the selection process was paused as a result of claims that local member data provided to some candidates was inaccurate, in addition to allegations that the membership database was tampered with.
An email sent to Labour members earlier this month, seen by Inside Croydon after the internal investigation concluded, said: "Our investigation has now shown that, from 8 September 2023 to 14 November 2023, some of the personal details of Labour members in the Croydon East constituency were altered on the Labour Party membership database without authorisation.
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"The personal details that were amended included e-mail addresses, telephone numbers and postal addresses.
"We can confirm that no sensitive personal data, such as financial data, was affected by this incident.
"As a result, you may not have received all Labour Party communications that we tried to send to you during this period, including information about the Croydon East and Croydon and Sutton selection processes."
The Croydon East constituency was abolished in 1955, but was re-established in 2023 following a Boundary Commission review.