A quote from The Sydney Morning Herald, 18 October 2008

Australian historian Dr Fredrick Toben will remain behind bars in Britain until October 29, when a judge decides whether the alleged Holocaust denier will be extradited to Germany. The academic, 64, was arrested while in transit at Heathrow Airport on October 1 under a European Arrest Warrant (EAW) issued by Germany, which wants to try him for his alleged anti-Semitic views. […]

Unlike in Britain, Holocaust denial is a crime in Germany and offenders can face up to five years prison.

 
A quote from The [London] Times, 2 October 2008

The [European Arrest Warrant], which came into force in January 2004, abolished the principle of “dual criminality” that existed under old extradition laws. This means that someone in Britain can be extradited for something that is not a crime here - as long as it is a criminal offence in the state requesting extradition.

The reform was rushed through in part as a response to terrorism after September 11. Ministers also argued that it would speed up a cumbersome and slow extradition process, helping criminals to be brought more swiftly to justice.

Critics pointed out, however, that people could find themselves charged with an offence they did not know existed because racism or xenophobia, for example, can be interpreted differently in different jurisdictions. The spectre of “thought crime”, a person facing trial for broadcasting xenophobic or racist remarks such as denying the Holocaust on an internet chatroom in another country - as alleged against Dr Toben - was the very criticism raised against the warrant before it took effect.

 
See also:

Negationist Negates German Prisons, 8 August 2005