Er, depending on your country, they are different things. In the UK, you can be detained by police for a short period of time (e.g. during a stop-check or search on the street), but it isn't an arrest, you're "just" prevented from leaving whereever you are for a short period of time. If you are arrested, it means you are taken to a police station where a whole lot of rights/procedures/paperwork kicks in. Different countries have different points where they hit the dividing line between detaining and arresting.

> If you are arrested, it means you are taken to a police station where a whole lot of rights/procedures/paperwork kicks in. Different countries have different points where they hit the dividing line between detaining and arresting.

I'm not sure that's true. On every UK police program I've seen (mostly traffic-related - Road Wars, Police Interceptors, etc), frequently they'll arrest someone at the roadside, then de-arrest them when they've finished their inquiries.

This is the first time I've heard the term 'de-arrest', but it does indeed exist:

http://www.theguardian.com/world/2006/mar/01/law.emmabrockes "According to section 30, subsection (7) and (7A) of the Police and Criminal Evidence Act 1984, to "de-arrest" is to allow that "a person who has been arrested under any act of law at a place other than a police station, shall be released before reaching a police station if a constable is satisfied that there are no grounds for keeping him under arrest". Unlike being released with no further action, being de-arrested means that the record of the initial arrest is removed."

It's definitely true (I used to be a UK cop). While there are situations where you can de-arrest someone after arresting them, it's rare, and you do not need to place someone under arrest to detain them. Many (minor) crimes are not "arrestable" offences, for instance a cop cannot arrest you for littering. However he can detain you while he ascertains your identity in order to issue you with a fixed penalty notice (ticket), after which you are free to go and have not been arrested/de-arrested, merely detained. If you refuse to co-operate by giving your details, or he believes you may have given false ones that you can't back up with ID, he can then arrest you under PACE regulations and take you to the station to confirm your identify. But he can't arrest you for the littering. But he can detain you briefly.

On the police shows you mention, when the officer stops a car and takes the person into theirs to check their driving license, search them etc. they are detaining them. Only when they tell them they are under arrest are they actually under arrest, and they need reasonable grounds to suspect them of an arrestable offence before they can do that.