Internet and phone voting pilots planned for local elections in May should be suspended until polling security is improved, a watchdog says.
Local elections are to be held on 3 May
Sir Alistair Graham, chairman of the Committee on Standards in Public Life, said the "integrity" of the current system needed to be safeguarded first.
He criticised the Department of Constitutional Affairs for experimenting with "high risk" systems.
But electoral law minister Bridget Prentice said he was "plain wrong".
Sir Alistair Graham made his remarks to a conference of returning officers.
He later told BBC Radio 4's World at One: "We believe that the department of Constitutional Affairs has got its priorities wrong.
"We should be concentrating on safeguarding the integrity of the current voting system rather than experimenting in remote systems which are bound to carry a high risk."
He also said the new system of checking signatures for postal votes also had "some issues".
He said it was inevitable that some signatures would be rejected by the software used for checking, leaving the decision up to the individual returning officer.
"I've called for these projects to be put on hold for the moment and I also want a guarantee that there will be a 100% check of signatures in the May elections."
He said he had argued for the voter registration system to change so that individuals were required to register rather than the current system where the head of a household can register everyone at an address - "which undoubtedly allows for possible fraud to take place because nobody checks whether that information is accurate".
Mrs Prentice said it was wrong for Sir Alistair to say the government had its priorities wrong.
"The government has shown deep concern about the integrity of the system which is why we made very considerable changes, not just after 2004 but again in 2006."
She said the changes for postal voters meant they have to apply again for their votes and send in a signature with their date of birth. Once they receive the vote they have to sign it with their date of birth, allowing the returning officer to check the signatures.
Mrs Prentice met with representatives from the Council of Europe, who are visiting Britain after a complaint from a Conservative MP about the security of postal votes and absentee ballots.
They are examining whether there is a need to set up a monitoring system by the council for the forthcoming elections.
She said of her discussions with them: "I hope they will be able to go back and see that we have put into place measures this May that show that we take electoral fraud very seriously, we take registration very seriously, and we want to see more participation in our elections by the people of this country."
Victorian voting system
But the changes to postal votes are expected to cause "some problems" on election night, said chief executive of Huntingdonshire District Council and a returning officer David Monks.
He said a minimum of 20% of signatures had to be checked, "but many of us want to check more than that to ensure there's as much security and integrity in the system as possible."
But he disagreed with Sir Alistair's call to suspend pilots.
"We have a very 19th century Victorian voting system in this country and we really have to push on and try some new methods of voting that fit our new lifestyle."
If no changes were made, then "it's a bit of a victory for the fraudsters, it's them saying to us 'look, we stopped you trying to make progress, we've stopped you trying to make changes that would benefit society'."