Downing Street has hit out at a human rights ruling saying that prisoners should get the right to vote.
The case was heard at the European Court of Human Rights
Tony Blair's spokesman said jailed criminals had lost the "moral authority" to participate in polls.
The European Court of Human Rights case was brought by lifer John Hirst, who is inside for manslaughter.
No 10 says the government will take time to consider the judgement before deciding whether to appeal against the verdict delivered on Tuesday.
Hirst, 53, admitted manslaughter 24 years ago but claimed he had a right to vote under the human rights convention.
He remains in prison as a result of a parole board judgement that he represented a risk to the public - although he is allowed out on day release.
The court said that national governments had the right to use discretion in interpreting the convention which ensures "the free expression of the opinion of people".
But a blanket ban, as applies in the UK, on inmates voting was not compatible with the convention, said the court.
Asked if the government was considering an appeal, the Downing Street spokesman said: "We do have to take time to consider the judgement before we announce what we are going to do.
"It has been the view of successive governments, and this one, that prisoners convicted of a serious enough crime to warrant imprisonment have lost the moral authority to vote - and that gives you a clear indication of what our attitude is."
Lawyers for Mr Hirst said he should have the right to vote under the convention's guarantee to the "right to free elections", the "right to free expression" and "prohibition of discrimination".
The judges delivered a unanimous verdict that denying a prisoner a vote does breach the "right to free elections" set out in the convention.
There was no need therefore, they said, to pass judgment on the issues of free expression and discrimination.
Hirst pleaded guilty on 11 February 1980 to a charge of manslaughter on the grounds of diminished responsibility.
He was sentenced to "discretionary life imprisonment" and the tariff part of his term - the part relating to retribution and deterrence - expired on June 25 1994.
He was awarded £8,000 in costs and expenses by the court on Tuesday.