A senior judge on the Court of Appeal has said he was shocked to discover that a 12-year-old boy who was repeatedly raped by his father had been cross-examined by a defence barrister for six days.

The criticism was made as the now 70-year-old man is appealing his conviction for raping his son from the time he was six years old.

The man, who is originally from the UK, was jailed for 14 years after a trial in 2016 at the Central Criminal Court. He was also convicted of cruelty by locking the boy in a box.

The boy's mother was convicted of child cruelty but acquitted of sexual assault.

On the opening day of the appeal, Mr Justice Patrick McCarthy said he was "shocked" by the length of time taken for the cross examination.

Ms Justice Isobel Kennedy said she found it "really difficult to see how you can possibly justify the length of cross examination of a 12-year-old boy".

Mr Justice McCarthy added that Colman Cody SC, who conducted the cross examination, had said before he started questioning the boy that he didn't know how long he would take. The judge said Mr Cody should have been able to make a "reasonably accurate estimate" and added: "That is a particularly acute problem where a child is concerned."

Mr Cody, who is now representing the man in his appeal, responded to the judges' criticisms saying that it was a "particularly difficult case". He said he dealt with the boy in a "respectful and measured way" but that it was a "unique case" where the allegations against his client were "particularly egregious".

Ms Justice Kennedy said the case was not "unique" and that the three judges of the Court had all dealt with similar cases. 

The appeal centres on the admission of evidence relating to a video of the boy's parents and at least one other person engaging in "raucous" sex acts at their home. Defence lawyers say this was prejudicial and was not relevant to the charge before the court as it was recorded six years previously. Mr Cody said the video depicted consensual sexual activity but the decision to allow a garda give evidence about it painted his client in a "particularly lurid and grotesque light".

Prosecuting Senior Counsel Pauline Walley argued the tape was consistent with aspects of the victim's accounts of how he was abused. He had described how his father sometimes video recorded the abuse. She said it showed the appellant was lying when he claimed there was never any pornographic material at his home following the birth of the victim.

Ms Walley said the evidence showed the recording was made following the birth of the boy and the appellant and others on the video could be seen viewing pornography, and pornographic material was also visible on a table. The evidence of the video was therefore probative and admissible, she said.

Mr Cody also said allegations made by the boy after he was removed from his parents' home initially only related to physical abuse. He said the allegations "evolved" into sexual abuse and he questioned the consistency of those accounts.

Ms Justice Kennedy said she could see nothing unusual in allegations coming out in the way they did. She added: "That is a regular type of situation in cases of this nature where disclosures come out on an incremental basis and increase in severity. That is quite the usual manner."

Mr Cody also complained that his client's previous convictions for theft of a jar of mustard and a paddling pool had been put to the jury. Ms Walley responded that the thefts were relevant because there had been an attempt by the defence to paint the accused as being a person "of the utmost probity and honesty" and to portray the boy as dishonest and untrustworthy.

During the lengthy trial in 2016, the court heard the boy was removed from the family home in 2011 and placed in a foster home where he was sexually abused by another child. This child was never prosecuted because he was below the age of criminal responsibility.

In March 2012 he was moved to another foster home where he was very happy. He began disclosing the sexual abuse by his father to his foster mother who documented it and handed it over to gardaí.

The foster mother "loved the child to bits", the court heard, but was forced to give up care of him because he was displaying disturbing behaviour. He was spying on her in the shower, acting inappropriately with other children and was obsessed with faeces.

Tusla, the Child and Family Agency, were forced to put him in specialised residential care in the UK as no suitable place was available in Ireland.

A psychologist said he was displaying highly sexualised behaviour but this has improved over time. The father was convicted of anally raping the child on nine occasions but acquitted of raping him with a poker. Other charges relating to allegations that the father forced the boy to have sex with his mother were withdrawn from the jury.

The boy described one occasion where his father was assembling a wooden box. He asked his father what it was for and the father replied "it's for you" before pushing him in. The boy was in there for three or four hours before his mother released him.

The appeal hearing continues tomorrow.