The ACT Court of Appeal yesterday invoked a rare ''Parker direction'' in the case of a man who subjected his children to sustained, horrific abuse over more than a decade.

The move meant the 56-year-old man's appeal against the severity of his 20-year jail term - one of the territory's longest in recent years - was over in moments.

Immediately after the court convened yesterday morning Justice Richard Refshauge said the bench considered Chief Justice Terence Higgins had erred in crafting the sentence.

But he said he and colleagues, Justice John Burns and Justice Bruce Lander, would consider increasing the original sentence on appeal.

A ''Parker direction'' gives an appellant faced with the prospect of a longer sentence a warning and a chance to withdraw the appeal.

The man's counsel, veteran barrister Ben Salmon QC, conferred briefly with his client before agreeing to drop the appeal.

Counsel for the prosecution, Director of Public Prosecutions Jon White, was not required to make oral verbal submissions.

The prisoner, who cannot be named for risk of identifying his victims, showed no emotion as he was escorted from the court.

At the sentencing last year, Chief Justice Higgins described the father as the ''instigator of profoundly evil behaviour'', aided by the children's mother.

He said the crimes were ''extremely serious and abhorrent''.

''They strike at the very foundation of civilised society,'' the judge said.

''They are offences committed by the very person or people that innocent children are entitled to expect love and protection from.'' The father ultimately pleaded guilty to 15 sexual offences; his wife admitted five charges.

The 58-year-old woman pleaded guilty to aiding and abetting her husband to engage in sexual intercourse with their daughters and herself committing acts of indecency and was locked up for 10 years, and will be eligible for release in 2015 after serving five. The abuse occurred at a home in the city's north between 1988 and 1999, began when the daughters were seven and nine and only ended when the victims left the family home.

During sentencing hearings, the ACT Supreme Court heard the abuse happened as often as every two days, and the victims were only allowed to leave the house to buy groceries.

According to court documents, the victims were home schooled until senior college, both parents were unemployed and would smoke cannabis in front of their children, the father would drink heavily and was on occasion abusive to his wife.

''The sexual abuse of these two courageous young women ... started when they were young children and continued until they were young women ...'' the Chief Justice said.