Confirmed it is a ransomware group.
My take would be the ransomware operator has made a mistake here as Leicester council have about 0% chance of being able to afford to pay - a year ago they described their existing budget as having a "near impossible cliff edge" to central government and they haven't received additional funding since - so the operator shoved the group's head into a beehive, the ransomware group should probably help them out.
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