The sacked chairman of the Northern Trust has demanded Health Minister Edwin Poots resigns after new figures revealed hospitals were still failing to meet waiting targets.
Four months after he was removed from the post following a public row over the targets, Jim Stewart said the figures proved they are "unachievable".
And he said despite new resources at Antrim Area Hospital, hundreds of patients are still having to wait more than 12 hours to receive emergency treatment.
In an interview with this newspaper, Mr Stewart claimed the figures not only "completely vindicated" his position, but the minister should "admit he was wrong, apologise – and then go".
The figures – which log weekly emergency department performance – revealed that during the month of March, Antrim Area Hospital had 299 breaches of the 12-hour waiting time. This is compared to 94 cases in March 2012.
The figures also showed regular breaches of targets.
From January 5-11, 132 people waited 12 hours or more at the emergency department.
This is despite additional nurses, additional consultants, additional beds and a team of experts in Antrim being installed since January, after the row erupted.
In March 2013, across the entire trust – that includes Antrim Area Hospital and Causeway Hospital – there were 427 patients waiting 12 hours or more for treatment at the emergency departments. The figures showed that during the week ending December 7, 2012 – the period leading up to Mr Stewart's sacking – 63.9% of patients were treated within four hours.
There were also 56 cases of patients waiting 12 hours or more at the A&E department.
A target was set by Mr Poots that 95% of patients attending any emergency department should be treated or discharged, or admitted within four hours of arrival.
But between March 4-8, 2013, there were 123 people waiting more than 12 hours in the emergency department, and 60.2% of patients were treated within four hours.
Last year Mr Poots said all trusts had to eliminate 12-hour waits in three months, adding that "heads would roll" if targets were not met.
A spokeswoman for the trust said during March that the Northern Trust's emergency departments received "a high number of attendances".
"Unfortunately, some patients had to wait longer than we would have liked. The trust has introduced a range of measures to improve access to unscheduled care," the spokeswoman said.
But Mr Stewart was critical of such targets and claimed they placed staff under immense pressure.
"They are unrealistic and unreasonable," Mr Stewart said.
"Despite having additional consultants appointed last year, additional funding and a team of experts from GB in Antrim since early January, the next month in Antrim 100 people were waiting over 12 hours in one week before they were admitted, and only 61% of all patients were seen in under four hours.
"After four months the figures have not improved. This verifies that my views were correct. This is despite extra nurses, extra consultants, extra beds and a team of experts in Antrim since January.
"I've gone – but nothing has improved regarding target times. Poots should admit that he was wrong," said Mr Stewart.
But the minister defended his policy. A Health Department spokesman said: "The public certainly do not share Mr Stewart's view that having people treated in emergency departments within 12 hours is 'unrealistic and unreasonable' or 'cannot be consistently achieved'."
He said the minister expected the support team "to impact positively" on waiting times at Antrim Area Hospital's A&E.