Haringey Council has been slammed by an ombudsman after it admitted having hundreds of unread welfare reports in an email inbox.
The Local Government and Social Care Ombudsman (LGO) revealed there were more than 1,100 unread emails in the council's social work inbox "including 500 police reports".
Julie Odams, the LGO's chief executive, said the council needed to make "lasting changes" following this "inertia".
In the report the watchdog refers to a case where a resident, who was at risk of homelessness and had health issues, didn't receive any help despite a friend reaching out - along with the emergency services - to the council.
The resident consequently "had a fall during a seizure" leaving him with "a life-changing injury".
Odams said: "Because of the council's inertia, the man at the centre of this case was left at risk of significant harm. While we cannot say the accident which caused such a major injury would have been prevented if the council had acted sooner, the man's friends and family are left not knowing whether things might have turned out differently if he'd had the help he needed earlier.
"The council has agreed to put in place an action plan to improve how it responds to safeguarding alerts like these, including training staff on dealing with safeguarding referrals. I hope this shocking case will spur the council into making lasting changes which will benefit other vulnerable people in the borough."
Liberal Democrat councillor Pippa Connor, the opposition group's spokesperson for social care, said the findings were "absolutely shocking" and "utterly negligent".
She said: "Haringey of all places should have failsafe measures in place when it comes to serious safeguarding issues like these. It seems inconceivable to me that managers were not aware of these longstanding issues prior to the ombudsman's intervention.
"Apologies are no longer enough: we have heard 'this must never happen again' too many times before."
Cllr Connor called for "senior officials and politicians" to explain what "robust monitoring processes" were "now in place" and "how this was allowed to happen".
In response, Lucia das Neves, the council's cabinet member for health, social care and wellbeing, said: "We recognise the seriousness of the findings and fully accept that mistakes were made, for which we apologise.
"We should have responded more swiftly when concerns were raised about the neighbour's health and vulnerability.
"A series of actions have already been undertaken to address the concerns raised about our handling of this case and we have cleared the backlog of unread emails highlighted in the report.
"We are approaching this with honesty, accountability, and a clear focus on improvement.
"The council is committed to learning from this case, and we are carrying out an independent review of our safeguarding arrangements to ensure that we are delivering the highest standards of care and support to our residents."
