Police subsequently laid the charges against the wrong man, but on September 10 Mercer presented himself at the Greymouth police station and confessed that he had duped the arresting officer.
Lawyer Richard Bodle yesterday sought bail for Mercer, saying that he had an appointment at Christchurch Hospital next Tuesday and could not miss it.
Judge Gary McAskill flatly refused bail, saying that Christchurch Prison staff would see that he kept the hospital appointment.
Mercer had eight previous convictions of driving while disqualified and 12 drink-driving convictions, and the judge said a prison sentence was inevitable.
"You are a menace on the roads and have delayed this since September and pleaded guilty at the last instant ... you have manipulated the system," the judge said.
"I'm not going to protract this process any longer; you are remanded in custody for sentencing on July 2."
Mercer, his legs seemingly crumbling under him, had to be assisted from the dock, asking the warden: "What's happening ... what did he say?"