England, Wales, and Northern Ireland:
- The legal blood alcohol concentration (BAC) limit is 0.08% (80mg of alcohol per 100ml of blood).
- Breath limit: 35 micrograms of alcohol per 100ml of breath.
Scotland:
- The legal limit is lower at 0.05% (50mg per 100ml of blood) and 22 micrograms per 100ml of breath.
UK police use breathalysers and other alcohol countermeasure systems to detect violations. Exceeding the limit can result in fines, bans, or imprisonment depending on severity and BAC level.