"that every person at any stage of an investigation should be able to communicate and to consult privately with a solicitor. This is so even if he is in custody provided that in such a case no unreasonable delay or hindrance is caused to the process of investigation or the administration of justice by his doing so; that it is a fundamental condition of the admissibility of evidence against any person, equally of any oral answer given by that person to a question put by a police officer and of any statement made by that person that it shall have been voluntary, in the sense that it has not been obtained from him by fear of prejudice, or hope of advantage, exercised or held out by a person in authority or by oppression; and when after being cautioned a person is being questioned, or elects to make a statement, a record shall be kept of the time and place at which any such questioning or statement began and ended ... Any questions put and answers given relating to the offence must be contemporaneously recorded in full and the record signed by that person or, if he refuses, by the interrogating officer."