I know enough about about British police procedures to say this is ridiculous. There is no way that anyone is thrown into a cell without having it outlined to them what they have been arrested for. That is the point of going to the custody desk when he arrived. The character would have been informed of his rights like legal assistance and to let someone know that he was there as well as access to medical help if he was injured or unwell. If any of this did not happen the police would have a legal case to answer. I watched about 40 minutes and just found it overwrought.