The pilot in question was conducting a line check or a safety pilot, so he was working and on duty. In this case he was NOT reported by any bartender, since he was breathalyzed after arriving from a flight from London.
Usually, if you're positioning / deadheading you are on duty so you should be sober. In this day and age, I would strongly suggest being sober at any time when you're wearing your uniform. You might be 'legal' but some faeces will definitely hit the ventilator when caught (bad press for company, tea&biccies with boss etc.)