Poor communication, understaffing and a "failure in the system" meant up to 200 Plymouth people were unable to vote in the General Election, a report has found.
Council chiefs have apologised after more than 1,500 postal ballots went missing in the run-up to polling day in June, while many people were turned away from polling stations and 6,000 votes were not counted on the night.
A detailed independent investigation has set out the reasons behind a catalogue of errors.
Dr Dave Smith who wrote the report says the council has long had a problem with "Insufficient capacity and capability within its core registration and elections service."
"As a direct consequence of the shortfall in capacity and capability, the registration and electoral operational system and process lacks integrity and robustness.
"The lack of a detailed operational procedure manual, the lack of experience and understanding of the current electoral management system, the lack of operational management grip, integration of tasks and the absence of effective quality controls, quality assurance and independent checking are critical points of failure in the system."
The fall-out from the mix-up has cost Plymouth City Council more than £68,000.
Dr Smith says the council "needs to take urgent action to review its recruitment strategy to attract appropriately skilled and experienced registration and elections staff".
"The council needs to act without delay to recruit additional permanent and technically capable staff to the core team and achieve a compliment of staff and management."
Acting returning officer Tracey Lee has apologised on behalf of election-night personnel.
"We accept fully Dr Smith’s conclusions and have already started the work to make our electoral service fit for purpose. We still have work to do but we are committed to getting this right."
Council leader Ian Bowyer has thanked Dr Smith and says his report is an important step in restoring voters' faith.
"It’s important for all councillors that both they and our voters have complete confidence in the council’s electoral service. I am totally committed to ensuring that this happens.”