By Nick Dermody
BBC Wales news website
So far South Wales Police say they have caught nearly 100 drink drivers during the first 10 days of their Christmas anti-drink drive campaign - almost double the number of arrests last year.
'Steve's' breath test at the police station was below the legal limit
With the Christmas party season upon us, the force is warning revellers not to drive for 24 hours after a heavy night's drinking.
During the morning I went out with Operation Sherry, it didn't take long for Tony, the police constable I was with, to add another collar.
Steve, a property developer from Cardiff, was spotted illegally using his mobile phone while waiting at traffic lights, something he denied. He was breathalysed. It tested positive.
And so, Steve, Tony and I made our way to Cardiff Central Police Station so the arrest could be processed.
The late rush-hour traffic seemed to part instinctively for us in the marked patrol car as our man blamed his predicament on not having had anything to eat the night before or that morning.
"I had four small glasses of wine at a business lunch yesterday," he said.
"And a bottle of wine in the evening - but I haven't had any supper." He didn't have any breakfast either, and was regretting it now.
After he is released, Steve picks up his personal effects
The roadside breath test put him at 36. The legal limit is 35. The three of us talk about his chances of him coming under the limit at the all-important second breath test at the station.
As the journey continues, Steve begins to deliberately hyperventilate, taking a series of rapid short sharp breaths. It is what a doctor once told him to do, apparently.
In the custody suite, the duty sergeant reads out the charge of suspected drink driving. Steve takes off his belt, empties his pockets and puts everything in a plastic bag.
"I don't drink and drive," he said. "If I'm drinking, I don't have my car, or I have someone drive me around. Had I eaten, I would not be here having this issue."
Steve is hyperventilating continuously as he answers the last of the official questions.
The machine decides it is warmed up and ready. Steve puts the tube to his mouth and blows. An alert sounds. The test was not done properly.
Safe to drive
Steve tries again. As he blows, Tony stands at his side and tells him to keep blowing. The test is valid.
The reading comes back as 21 - well below the legal limit, but showing there is still alcohol in his system.
A second test comes back as 20. The lower reading is what a court would consider, but Steve is free to go.
As we give him a lift back to this car, Steve is insistent he was always safe to drive. Tony thinks otherwise.
He said: "We just scrape the surface of the problem of people who think they are okay to drive when they've still got alcohol in their system from the night before - there must be loads more."