David Cameron has set up a clash with Europe by signalling he will fight plans to force the UK to give prisoners voting rights.
At Prime Minister's Questions, he insisted the controversial issue should be a question for Parliament and not for a "foreign court".
He told MPs he backed their overwhelming vote last year against lifting the absolute ban against votes for prisoners.
"I have always believed when you are sent to prison you lose certain rights and one of those rights is the right to vote," Mr Cameron said.
"Crucially, I believe this should be a matter for Parliament to decide, not a foreign court. Parliament has made its decision and I completely agree with it."
His comments came 24 hours after the European Court of Human Rights (ECHR) ordered the British Government to change the law within the next six months.
In a ruling on an Italian case, the ECHR admitted that it was up to national authorities to decide exactly who can vote from jail - but said denying voting rights to all inmates indiscriminately is illegal.
The ruling is effectively a challenge to the British government to scrap the total ban and agree parameters about which prisoners will be able to vote.
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."
Following the new ruling on Tuesday, the Cabinet Office said the Government would be carefully considering the judgment and its implication.
The ECHR said that pending claims by UK prisoners - which number around 2,500 - will be struck out if Britain complies with the order before the deadline.
But Tories have reacted angrily to the judgment and said it is an infringement of parliamentary sovereignty.
Labour has also now pledged to support Mr Cameron if he chooses to defy the ultimatum.