The European Court of Human Rights has ruled that governments can decide for themselves how to oversee votes for prisoners.
In a ruling on an Italian case, the court said it was up to member states how to implement the ban - in what is a victory for Prime Minister David Cameron .
Mr Cameron has been given six months to honour the Government's pledge to give prisoners the vote and the decision means he now has the freedom to decide how it will work.
The court said it now accepted the UK government argument that "each State has a wide discretion as to how it regulates the ban, both as regards the types of offence that should result in the loss of the vote and as to whether disenfranchisement should be ordered by a judge in an individual case or should result from general application of a law."
The UK was given nine months to introduce at least partial voting rights for some prisoners in November 2011 but has not done so.
The deadline was extended after the UK authorities asked to make legal submissions in the Italian case, and a new six-month deadline has been triggered by the ruling.
The wrangle with Strasbourg began when UK inmates complained that the loss of voting rights violated a Human Rights Convention Article guaranteeing the "right to free elections".
The court twice decreed the UK's total ban on votes for prisoners to be illegal but the Labour government left the ban in place, and Tory inaction despite a second ruling in 2010 angered civil liberties groups.
Last autumn, Minister for Political and Constitutional Reform Mark Harper told the Commons that the coalition reluctantly accepts that the UK has a legal obligation to fall in line, but has not yet decided which inmates it would affect.
Mr Cameron was more direct, telling MPs: "It makes me physically ill to contemplate giving the vote to prisoners. They should lose some rights, including the right to vote."