I can only assume things in Scotland are dealt with differently to England, with regards to insurance and MOT related offences.
Firstly, I'm trying to get my head around why the visit to the nick was considered necessary. In england, MOT and insurance offences can be promptly dealt with at the roadside in most cases, providing the Identity of the driver is confirmed. You could either be issued a fixed penalty, reported for the offence (court date arrives in the post), and vehicle seized.
Were you actually arrested, or was it a voluntary attendance?
Again, unsure of scotland, but in England and Wales, anyone stopped without insurance could have their car seized under S165 road traffic act.
A vehicle cannot be seized as such for no MOT in England, unless an officer (usually traffic) decides it needs to be prohibited from use for a specific safety reason.
It seems crazy that, they process you because they believe you have no insurance, but then let you drive said car home, uninsured, for 400 odd miles!
Most british forces now have a non-endorsable fixed penalty for no MOT. 60 quid and no points. If stopping someone for no MOT, whose insurance is otherwise in order, it would seem like two bites of the cherry to try and stick them on for no insurance as well...
Not having much luck are you
