VITAL election documents were found in the middle of a road after falling from the back of a lorry.
The box, containing papers for Thursday’s elections, was handed in to police after it was discovered in Belvedere Road, Ashbrooke.
Although no ballots were contained in the sealed box, the papers included the dates of birth and signatures of voters.
Investigations found it fell from the back of a Gentoo van while it was being transported from Sunderland Tennis Centre to the civic centre following verification ahead of Thursday’s count.
Politicians today called for a full investigation into the incident.
Coun Paul Dixon, a Liberal Democrat running for re-election in the Millfield Ward, said: “I’m disappointed that something like this has occurred. It is embarrassing for the council.”
Dave Smith, Sunderland City Council’s chief executive and election returning officer, said: “It is believed that the weight of the container may have pushed open an unlocked rear van door.
“This is the first time anything like this has ever happened in Sunderland.
“The container was in a sealed condition when it was handed into Northumbria Police at Gill Bridge Police Station by a member of the public.
“As council staff unloaded the van, they were contacted by police. The numbered seal on the container was not broken and its contents not disturbed.
“The contents have been verified and we can confirm that nothing is missing.
“We would like to thank the public-spirited person who handed this container in.
“As a result of this unfortunate incident, the council has reviewed its procedures to minimise the risk of this happening again, and informed the Electoral Commission.”
The council added the papers would have been available for public inspection following Thursday’s final count.
Among those to refer the incident to the Electoral Commission is the UK Independence Party, which has seven candidates running this year.
Richard Elvin, chairman of the party’s North East branch, said: “The loss of material relating to postal ballots is a serious matter a lawful democratic process and calls in to question the transportation of papers.
“We expect Northumbria Police to stage a full investigation.
“We’ve been told the Electoral Commission that from the information provided, they are happy with the security of the papers.
“I’m sure it’s probably OK, but I think something as important as this should be fully investigated, because what would have happened if it had been ballot papers?”
Council leader and Labour member Paul Watson said: “It’s just unfortunate that we’ve had something like that happen. “It’s one of the most fundamental and tenacious parts of democracy, not being able to tamper or interfere with the voting process.
“But it is reassuring that this public-spirited person handed this in.”
Coun Dixon added: “I would definitely call for an investigation but I would say I’m surprised because to give the council its dues, the elections are really well run and it does a good job.”
Coun Robert Oliver, leader of the city’s conservatives, added: “It’s a mistake on someone’s part and we were concerned, but we feel it’s not an issue which will affect the outcome of the council election and we are happy that it’s been recovered.”
Ian Porter, managing director of Gentoo Sunderland, added: “On Friday afternoon we were alerted that a container had been found and was being held at a local Police station.
“The container containing postal vote statements was sealed and intact and there was no damage to the contents.”