Fire safety checks will need to be redone on more than 1,600 council homes, because of concerns previous inspections may have been conducted by unqualified officials.
The revelation is the latest twist in a long-running saga, which emerged last year when Norwich City Council admitted hundreds of people in its properties were potentially put in danger because crucial safety inspections of fire, water and electrics had not been done.
Since then, £1.2m has been spent clearing those backlogs and all overdue gas checks, as well as the majority of electrical tests have been completed.
But a report which will come before the council's cabinet on Wednesday reveals a further complication has been identified.
City Hall officers could not be sure about accuracy of data about historical fire risk assessments which had been carried out in low-risk buildings.
They said inspections "may not have been completed by suitably qualified individuals".
So, 1,615 inspections will need to be redone and people in those homes will be contacted and fresh visits arranged.
Labour-run Norwich City Council had paid contractors, including Norfolk County Council-owned Norse, to carry out such checks, going back several years.
But last year it discovered many had not been done, or completely incorrectly.
Letters were sent to 17,000 tenants and leaseholders in October to tell them inspections had not happened and would need to be done.
Council leader Alan Waters acknowledged the buck stopped with the council - which had oversight for the contracts.
And the government’s Regulator of Social Housing said the council had “failed to meet statutory health and safety requirements in relation to fire, electrical, asbestos and water safety”.
A city council spokesperson said: “Considerable progress has been made across all safety areas since the work programme began last November.
“As things stand, all overdue gas safety inspections are now complete as are the majority of electrical inspections, including remedial actions.
“As an additional measure to show our firm commitment to achieving 100pc compliance across all safety areas, we will be entering into something called a ‘voluntary undertaking’ with the housing regulator.
“This is an agreement which confirms the steps we’ll take to achieve full compliance – when that is completed the regulatory supervision will be lifted.”
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