David Cameroon threatened today to defy the European Court of Human Rights and his own Attorney General by not giving prisoners the vote.
Mr Cameron told the Commons: "No one should be in any doubt. Prisoners are not getting the vote under this government."
It followed reports that the coalition was drafting a new law to give inmates ballot papers.
But Attorney General Dominic Grieve told justice committee MPs earlier that the Euro- judges' ruling "imposes an international legal obligation on us."
He said Britain had to obey them or face huge damages claims.
A government guided by common sense would respond to news that publicly owned Royal Mail has increased profits to £403 million by scrapping plans to flog off the service.