In my Policing day (20 years ago now) if a person failed the roadside test, and then were found to be over the prescribed limit on the intoximeter machine at the Police office, then they were only released after signing an undertaking to present themselves at the local Sheriff court on a date within 7 days. At court, it was up to the accused person whether they pled guilty or not guilty.
Guilty and obviously an immediate ban. Not guilty would result in a trial date being set several months down the line. The accused could be given conditional bail in the meantime, and one of the conditions imposed was that they were not allowed to drive. So effectively a ban.
Where this all falls down though, is the lack of proactive Policing. Drivers who have been banned for whatever reason continue to drive, safe in the knowledge that the chances of being caught are very slim. Unless they do something stupid under the nose of the Police.
When was the last time anyone here was stopped randomly for a Police check? I have been driving for 40+ years (averaging about 15k miles per year - car, motorbike, and HGV's for 10 of those years) and it has NEVER happened. Two VOSA checks while driving HGV's, but they weren't interested in my licence.