 If he is detained for the purpose of enabling him to be brought before a justice, the fact that he is questioned, whether about the offence for which he was arrested, or about other offences, will not necessarily mean that there has been a failure to bring him before a justice as quickly as was reasonably practicable.On the other hand, if he is detained, not for that purpose, but solely for the purpose of questioning him, the detention will be unlawful.The line may be a fine one, as it often is when a discretion has to be exercised in sensitive matters."