Something that I have wondered about (on a theoretical level, not personal, btw) is a situation that is very possible where I live ref the different permitted levels...
Pre-observation #1: I *think* the various Police Services in the UK only have primary jurisdiction in their own operational area? So say a Met Police car chasing someone would hand over to a Thames Valley car once it went past a certain point on the M4 (and maybe Surrey Police in-between?) - unless they had prior permission to continue.
I also think this would be particularly so when crossing a Country Border where depending on direction of travel, Police Scotland would either take over or relinquish responsibility for apprehension, given different laws - and knowledge of those laws - may be applicable.
The nearest town to me is Coldstream. There are quite a few pubs there. Coldstream is in Scotland.
The nearest village to Coldstream is Cornhill. I am not sure if there is more than one drinking establishment in Cornhill. Cornhill is in England.
Cornhill resident drives to Coldstream, has a pint of lager and that takes him to an alcohol level of 70. He then proceeds to drive back home. If he was in England, he is under the limit. As he was in Scotland, he is over the limit.
sets off out the carpark and heads home. Now from the pub to the Border is maybe a mile at the most, so a very short time will be taken (important point).
A Police Scotland car sees him leave the pub and follows him and decides to pull him over as his brake lights are not working.
The driver decides he does not want to risk a breathalyser so continues over the bridge and pulls over for the police car into the layby, which happens to be just over the "welcome to England" sign (and quite a way past the "Welcome to Scotland" sign in the other direction as it happens).
1) Can the Police Scotland car continue the follow over the Country Border?
2) If they do, can they actually make a charge without the person first returning to Scotland? Note due to short distance there is no way they could have got permission from Northumberland Police to cross Border in their role as police.
3) If they detain the person to wait for local English Constabulary to attend, what then happens? The Brake Light offence is clear cut, but if they (either/both Police Services) suspect the driver of drinking, what happens? Can Police Scotland breathalyse someone in a different jurisdiction? If they pass that role to the other Police Service, their breathalyser is calibrated at a different level so the driver would pass.
4) Can they request (and would it be legal to do so) that the English Police officer escort the driver back over the border so that Police Scotland officer can test them in Scotland?
I find it an interesting question and this actually came to mind a few years ago when another law was passed in Scotland related to a situation regarding Smoking in a car with Minors, where no such law existed in England. The same scenario (but for a much more serious issues IMO) applies here.
But still doesn't change the fact ... don't want to do the time, don't do the crime.