The campaign group had official observer status at the English and Scottish elections in May.
The ORG said e-voting was a "black-box system", where the mechanisms for recording and tabulating the vote are hidden from the voter. "This makes public scrutiny impossible, and leaves statutory elections open to error and fraud", said the group.
The 2007 English pilot e-voting programme was announced by the Department for Constitutional Affairs in October 2006, but official notice of approved schemes was not given until January 2007, three months before the pilots were due to run, said ORG.
This provided authorities with insufficient time for considered procurement processes to be conducted. The resulting schedule was completely inadequate for development and implementation of robust live systems, especially considering that they involved immature technologies, says the report.
The e-voting and e-counting technologies deployed did not perform to the standards expected by returning officers (ROs), candidates and their agents.
Inadequate attention was given to system design, systems access and audit trails. Systems used both inappropriate hardware and software, and were insufficiently secured.
Problems included machines in public areas with open ports, informal transfer of files using personal devices, and single-factor authentication, says ORG report.
"On election day, vendors provided many assurances regarding progress to ROs that were all too frequently not met," states the report.
Technical staff at South Bucks were instructed not to communicate with ORG observers.
In Swindon, an ORG observer received conflicting reports from a presiding officer and a contractor about the status of what appeared to be malfunctioning voting equipment.
Software supplied by suppliers incorporated elements that were dated and subject to known security vulnerabilities. "This could have been prevented by a rigorous certification scheme for equipment and software, and the lack of such certification is of significant concern," said ORG.
In Swindon, laptops at polling stations used for e-voting and live electronic registers proved unreliable, with the majority of polling stations experiencing problems.
At Rushmoor, the ballot platform displayed incorrectly at the opening of advanced voting and electors reportedly experienced problems with error messages.
Online voters in Sheffield also had trouble casting their votes. Where they existed, cryptographic receipts were generally poorly designed and difficult for voters to use.
ORG received a number of reports concerning difficulties in understanding and using the telephone voting system in South Bucks, and in understanding the registration process in South Bucks and Rushmoor.
Chaotic scenes were observed at the English e-counting pilots, with very significant delays in the declaration of results. Scanner malfunctions and software errors slowed counts and the adjudication process.
Scanner sensitivity to poor-quality printing, incorrectly cut paper sizes, fold marks and tears from low-quality perforations all contributed to the high number of ballots sent for adjudication.
The result of these problems was that pilots in Breckland and Stratford abandoned e-counting in favour of a manual count.
In Breckland, manual recounts - insisted upon by an election agent - revealed major discrepancies between the numbers counted manually and electronically.
Breckland’s Dereham-Humbletoft ward, the one ward in England that was counted both electronically and manually, was found to have 56.1% more district council votes than when e-counted.
Sixteen Scottish parliamentary constituencies declared results where the number of spoilt ballots was greater than the winning margin.
“Given the problems observed and the questions remaining unanswered, the ORG cannot express confidence in the results declared in areas observed.
ORG remains opposed to the introduction of e-voting and e-counting in the UK,” says the group.
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