A student died after he downed a bottle of rum in 15 minutes for a bet during Freshers' Week.
Timothy Jarvis, 18, had just begun a maths degree at the University of Essex when he fell down a flight of stairs and smashed his head in October 2011.
The teenager, from Orpington in Kent, was taken to Colchester General Hospital but had to wait almost 90 minutes before being assessed because the ward was short-staffed.
He was later transferred to the specialist neurological unit at Queen's Hospital in Romford, where he died.
Now the Evening Standard has revealed that Colchester hospital and Timothy's mother Marina Jarvis, 55, contacted the General Medical Council with concerns about one of the three middle-grade doctors on duty the day Timothy was admitted.
Ms Jarvis claimed the doctor failed to examine her son and later was wrong when he described her son to the inquest as 'laughing with friends'.
A report commissioned by the coroner at Ms Jarvis's request stated Timothy's death could have been avoided if his airway had been managed properly.
Another report said the care provided 'fell seriously below' the expected standard.
The GMC told the doctor that it 'may decide to conclude with a warning', but the doctor refused to accept one and a panel ruled in his favour at a hearing last week.
In evidence, the doctor's barrister Edward Pleeth argued the emergency department was busy and understaffed.
The hearing was also read statements from other staff members who corroborated the doctor's evidence that Timothy was conscious on arrival and not in urgent need of care.
The panel accepted the doctor was trying to prioritise care for the patient and was acting in his best interests.
Ms Jarvis told the Evening Standard she would complain to the manager of the investigations and complaints committee at the GMC.
A spokesman for the Colchester Hospital University NHS Foundation Trust, which runs Colchester General, said it had carried out a 'thorough' investigation and implemented improvements.