David Boothroyd, cabinet member for Finance and Council Reform, said: “I want to reassure residents that we are doing everything possible to respond effectively to the cyber security incident and to keep delivering our services.
“Our priority is to support and protect the most vulnerable in our community, despite the disruption that is being caused.”
“We acted quickly to secure our systems, and we are working towards restoring council services as safely and swiftly as possible, but this will take time. We remain committed to transparency and will continue to provide updates as our recovery progresses,” he added.
Kensington and Chelsea Council said it may take “months” for services to return to normal.
Council leader Elizabeth Campbell said the authority would carry out a review “when the time is right”.
Hammersmith and Fulham Council, the third authority to be impacted, said there is no evidence to date that its systems have been compromised.
Westminster City Council is urging residents to be extra cautious with unexpected calls, emails or texts and to follow official guidance from the National Cyber Security Centre.