John Hogan has won permission to launch a High Court challenge against the inquest verdict that he unlawfully killed his son.

The mentally unstable father from Bristol threw his two children off a hotel balcony, killing his son Liam, while the family were on holiday in Crete in 2006.

Yesterday, two judges ruled that Hogan's case raised "serious points that are plainly arguable" and gave him permission to seek a judicial review.

Hogan wants to overturn Avon coroner Paul Forrest's ruling earlier this year that his six-year-old son Liam was "unlawfully killed".

But his former wife, now called Natasha Visser, was "distressed" by the prospect of the review, her family said yesterday.

Former tiler Hogan, 34, of Bradley Stoke, pushed Liam and his two-year-old sister, Mia, before jumping himself following a row with Mrs Visser.

Liam died, but Mia survived the 50ft plunge from the fourth-floor balcony whilst on holiday in Crete.

Hogan was cleared of murder after a trial in Greece, when a jury decided he had been suffering from "an earthquake of insanity", but is being held in a psychiatric unit for an indefinite period.

Hogan, acting through his sister and with the benefit of legal aid, yesterday asked Lord Justice Dyson and Mr Justice Griffith Williams, sitting at London's High Court, for permission to seek court orders quashing the verdict.

His lawyers argued it was an irrational decision, wrong in law and based on insufficient evidence. The coroner was not represented at the hearing.

Giving permission for a judicial review, Lord Justice Dyson described it as "a tragic case".

He described how the family were holidaying at the Petra Mare Hotel at Ierapetra, Crete, in August 2006, when Liam's death occurred.

The Hogan marriage was unhappy. Before the balcony plunge, an argument had started between the couple and the then Mrs Hogan said she intended to leave her husband and take the children with her.

The judge ruled: "In my judgement it is, to put it at its lowest, arguable that the coroner was wrong to regard Mr Hogan's 'mens rea' (whether or not he actually intended to commit a crime) as irrelevant (to his verdict)."

James Badenoch QC, appearing for Hogan, had argued that the evidence pointed to the conclusion that "Mr Hogan was insane within the meaning of English law" and so did not have the required mens rea, or criminal intent, to kill his son.

Alternatively, he argued the available evidence cast doubt on the issue.

Lord Justice Dyson agreed, saying two Greek psychiatrists had examined Mr Hogan. But it was not entirely clear – "at any rate to the eyes of an English lawyer" – precisely what they were saying about whether or not Mr Hogan understood what he was doing was wrong.

"It seems to me it is not possible for this court to be sure what the outcome of further exploration of the psychiatric evidence would have been, and how it would have impinged on the issue of insanity".

The judge concluded: "In my judgment this application raises serious issues which are plainly arguable and which should be thoroughly aired at a contested – as I assume it will be – judicial review hearing."

Hogan's older sister, Christine O'Connor, from St George, Bristol, made yesterday's successful application.

Mrs Visser, who has married again, was not represented or present.

Her stepfather Brian Chandler said: "It is hard on Natasha who has to continue to worry about this again.

"Her priority is to help her daughter, Mia, working on her psychological recovery, as well as her own.

"It is very distressing for her to have this all dragged up again.

"But in terms of reaction to the appeal decision and Hogan, we have been advised against saying anything."

"This request for an appeal has absolutely nothing to do with what happened.

"It is purely a legal argument between the coroner and Hogan's legal team.

"It does not really have anything to do with the events of the day.

"There is no real evidence, in any court of law, which will change what occurred."