Legal action is being considered which could stop the Scottish Parliament election from taking place because prisoners are excluded from voting.
Prisoners are currently banned from voting
It follows a ruling at the Court of Session in Edinburgh that the elections would be incompatible with the European Convention on Human Rights.
The UK Government had set up a consultation process following a European Court ruling in 2005.
But legislation would not be introduced before Scotland's elections in May.
It is understood that a number of prisoners are already undertaking legal action to prevent the poll from taking place.
Three judges at Scotland's supreme civil court issued a declaration that the blanket ban on convicted prisoners voting was incompatible with their human rights.
A former prisoner, who was denied the right to vote in the last elections for the Holyrood parliament, took his case to the Registration Appeal Court in Edinburgh.
Lord Abernethy, who heard the appeal with Lord Nimmo Smith and Lord Emslie, said the May elections would take place in a way which was not compliant with the European Convention on Human Rights.
The judges said they had come to the view that they "should make a formal declaration of incompatibility to that effect".
The appeal arose after a serving prisoner, William Smith, had his application to be included on the electoral roll in 2003 rejected.
Lord Abernethy said Mr Smith's case was "of far-reaching importance".
"It is accepted by the government that there will be no amending legislation before the Scottish parliamentary election in May 2007," he said.
"We fully understand why the Government does not at this stage wish to rush forward with amending legislation but the fact remains that the Scottish parliamentary election in May 2007 will take place in a manner which is not Convention-compliant."
In 2005 a prisoner in England, John Hirst, who was serving life for manslaughter, won a decision over voting rights at the European Court of Human Rights.
Scotland Office Minister David Cairns said: "Today's judgement is not unexpected; it is consistent with the European judgement in the Hirst case."
He added: "We do not believe that the declaration will affect the operation of the Scottish Parliament elections.
"The conduct of the elections in Scotland is governed by UK legislation and all the legal detail of exactly how the elections go ahead are fully in line with the relevant UK law.
"Therefore we don't anticipate prisoners would be able to find sufficient grounds to successfully challenge the legality of elections. In line with the Scotland Act, the Scottish Parliament elections are being overseen by UK Government ministers."
SNP justice spokesman Kenny MacAskill hit out at the decision and said: "This is utter nonsense.
"The European Convention on Human Rights should be about protecting people from cruelty, harm and ensuring equality for law abiding citizens, not giving the franchise to those who do not respect the law and commit serious offences."
However Jo Swinson, the Liberal Democrat's Westminster Scottish spokeswoman: "The right to vote is fundamental in a democracy."
She said Britain was one of the only countries in Europe to impose a blanket ban on voting for prisoners.
She said: "We agree that those guilty of the worst crimes should not be allowed to vote.
"However, the Government's current position is unreasonable and has rightly been declared illegal."
Scottish Conservative justice spokesman, said: "On the basic issue of whether prisoners should be allowed the right to vote, the answer is a resounding 'no'.
"Many of their victims will have lost the capacity to vote, as a result of the crimes committed against them."