The government has resisted calls to allow prisoners the vote
Criminals jailed for less than four years could be given the right to vote under government proposals.
Ministers have been forced to lift the traditional ban on inmates voting to comply with a European court ruling.
But they stress the most serious offenders will still be banned from casting a vote.
The Tories urged ministers to keep the ban - but the Liberal Democrats accused Labour of lacking the "courage" to scrap it sooner.
The move is a potential embarrassment for Labour which accused the Lib Dems of being "soft" on criminals when they called for prisoners to be given the vote at the 2005 general election.
But the government's hand has been forced by the European Court of Human Rights in Strasbourg, which ruled in 2004 that the 140-year-old ban was unlawful.
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Those who have been removed from society for breaking the law have no right to a say in who makes the law
Justice Minister Michael Wills said: "The government has made it clear that it disagreed with the European Court of Human Rights ruling.
"However, the result of the ruling is that some degree of voting being extended to some serving prisoners is legally unavoidable. But, importantly, the government does not propose to give all prisoners the vote.
"We will ensure that whatever the outcome of this consultation, the most serious and dangerous offenders held in custody will not be able to vote. Prisoners sentenced to more than four years' imprisonment will not be permitted to vote in any circumstances.
"We believe this is compatible with the court's judgement and reflects the expectation of the British public that those guilty of the most serious offences should not be entitled to vote while in custody."
The government has promised MPs a vote on how the new law will be implemented.
It says the more serious the offence committed, the less right an individual should have to retain the right to vote when jailed.
It sets out a range of options from sentences of one to four years in a consultation, which runs until the end of September, although it says it favours the lower end of that scale.
Another option would be to give inmates serving under two years the automatic right to vote but allow judges to decide on those sentenced between two and four years.
But it does not plan to extend voting rights to prisoners released early or on a "life licence".
About 45% of the prison population, or 28,000 inmates, would be enfranchised if voting rights were given to all inmates serving fewer than four years.
The government plans to launch a separate consultation on giving voting rights to inmates detained under mental health legislation.
Shadow justice secretary Dominic Grieve said many people would "question whether this is a sensible development".
He told The Daily Telegraph: "The principle that those who are in custody after conviction should not have the opportunity to vote is a perfectly rational one.
"Civic rights go with civic responsibility, but these rights have been flagrantly violated by those who have committed imprisonable offences.
"The government must allow a parliamentary debate which gives MPs the opportunity to insist on retaining our existing practise that convicted prisoners can't vote."
But the Liberal Democrats accused the government of failing to fulfil its human rights obligations.
The party's justice spokesman, David Howarth, said: "The government has already had five years and a lengthy consultation on prisoner votes, but ministers have not had the courage to act.
"They now intend to have another consultation without any prospect of legislating on the issue.
"It is unacceptable for the government to pick and choose which human rights treaty obligations it fulfils just because it feels the issue is unpopular.
"While there are strong arguments that some prisoners should be denied the right to vote, this should be explicitly part of the sentence given by the judge."
The European Court of Human Rights ruled the law was incompatible with Article 3 of the European Convention on Human Rights, which guarantees the right to free elections.
The case was brought by John Hirst, who served 25 years in prison for killing his landlady and who accused the government of "abusing its power".
Mr Hirst was reported to be preparing a judicial review of the UK government's failure to implement the EU ruling.