European Convention on Human Rights
All members of the Council of Europe (which includes nearly all European countries and every member of the European Union) have adopted the European Convention on Human Rights. The optional Protocol No. 7 to the Convention, Article 4, protects against double jeopardy: "No one shall be liable to be tried or punished again in criminal proceedings under the jurisdiction of the same State for an offence for which he or she has already been finally acquitted or convicted in accordance with the law and penal procedure of that State."
This optional protocol has been ratified by all EU states except three: Germany, the United Kingdom, and the Netherlands. In those member states, national rules governing double jeopardy may or may not comply with the provision cited above.
Member states may, however, implement legislation which allows reopening of a case in the event that new evidence is found or if there was a fundamental defect in the previous proceedings:
The provisions of the preceding paragraph shall not prevent the reopening of the case in accordance with the law and penal procedure of the State concerned, if there is evidence of new or newly discovered facts, or if there has been a fundamental defect in the previous proceedings, which could affect the outcome of the case.
In many European countries, the prosecution may appeal an acquittal to a higher court. This is not regarded as double jeopardy, but as a continuation of the same case. The European Convention on Human Rights permits this by using the phrase "finally acquitted or convicted" (emphasis added) as the trigger for prohibiting subsequent prosecution.