In the UK, prisoners objecting to extradition can draw on protections guaranteed by the European Court of Human Rights. These include:
Article 3 which guarantees the right to freedom from torture, inhuman or degrading treatment or punishment;
Article 6 which guarantees the right to a fair trial;
Article 10 which guarantees the right to freedom of expression; and
Article 14 which prohibits discrimination on, amongst other matters, political views.
I wonder how many of these tests Turkey is capable of passing.
[P.S. The ECHR is not part of the EU so we remain participants in it post-Brexit.]