SECURITY chiefs have been trying to assess the damage caused this week by a cyber attack on Westminster City Council.

A number of systems were disrupted including phone lines but it was not immediately clear if the attack had compromised residents’ information.

Multiple councils were affected by the attack that was first noticed by the Royal Borough of Kensington & Chelsea who informed the Information Commissioner’s Office.

GCHQ is monitoring the situation.

Graeme Stewart, head of public sector at Check Point technology specialists told Sky News: “What’s happening here has all the signs of a serious intrusion: multiple boroughs knocked offline, shared infrastructure exposed, and urgent internal warnings telling staff to avoid emails from partner councils. That’s classic behaviour when attackers get hold of credentials or move laterally through a shared environment. Once they’re inside one part of the network, they can hop through connected systems far faster than most councils can respond.”

A spokesperson for the National Cyber Security Centre, part of the GCHQ intelligence agency and responsible for helping United Kingdom public bodies with cyber security, said: “We are aware of an incident affecting some local authority services in London and are working to understand any potential impact.”

A memo to council staff said that the authority is not predicting a full return of all affected systems “for some days”.

It also urges staff to “remain vigilant”.

RBKC first reported the cyber incident on Wednesday and has said it has been working with National Crime Agency and NCSC.

A spokesperson for Westminster Council said: “We are investigating the cause of the incident and will provide more information when available. We would like to apologise for any disruption and thank residents for their patience as we work to bring systems back online safely.”

An internal RBKC memo, seen by the Local Democracy Reporting Service said the council is keeping parts of its networks closed as a “precautionary measure”.