This seems a new one. http://www.bbc.co.uk/news/technology-18102793
If the report is to be believed then the police are planning to take all the data on an arrested person's phone and keep it indefinitely regardless of whether the person is charged or convicted and regardless of whether the data is relevant to the investigation or keeping it is justified for reasons of future intelligence.
This is plainly a serious breach of Article 8 of the ECHR. Does anyone know more? I am pretty sure there has been no legislation to legalise the practice so presumably it is the police again going beyond the law until they are stopped.