Bob,
They are mainly cases where the offence is a civil one, therefore they are mostly taxation based offences.
Detention without charge, within prescribed time limits, is allowed under The Police & Criminal Evidence Act. Extentions to that are allowed on application to a Judge.
I can assure you that officers in my department do not act on 'a whim' but entirely within the law. Those that don't, and like all organisations we have had bad apples over the 800 years since our creation, get thrown out and the full weight of the law is brought to bear.
I can't see the injustices that you see in the system but if you see them then you should protest. It is only because of that that we are not saddled with some of the rather more unpleasant legislation that has exsisted though history. There is as big and as equal a role to play for those who seek change as those that enforce the status quo. Many of the powers that you rail against date from the time of King Charles II. Prehaps you are right to argue for change. However whilst I am asked by my department to act and that request is a lawful one then I will do what is required of me and by the letter of the law and with due notice to official guidance. It is at times dangerous (8 C&E officers have died on duty in the last 20 years), long hours and unpleasant working conditions. and you certainly have to see things that no person should have to see. All the officers in my department do this. There's no space for those that don't.
If I felt the percieved injustices as you do then I would be standing at your shoulder but what I do is lawful and my concience is clear. Where I do stand at your shoulder is ensuring that your questioning of the system and the status quo is allowed a voice.
As Voltaire said (approximately) I'll disagree with you but I'll fight for your right to do so.
Guy