The idea is important because the most fundamental human right is freedom from arbitrary arrest. If the EU can impose this on us, it is hard to see how we can resisst any further encroachment upon our liberties. Already the idea of EU surveillance of political activists has been raised by the EU.
Our membership of the EU makes us subject to the European Arrest Warrant. This allows UK citizens to be deported to other EU states and imprisoned until their cases are tried. No evidence needs to be presented to UK courts or police. Arrests can be made for something which is not an offence in the UK