Jack Shepherd, the so-called speedboat killer, has argued that police made a mistake in failing to caution him when interviewed, rendering his manslaughter conviction unsafe.
The 31-year-old is serving a six-year sentence for the death of Charlotte Brown, 24, who was catapulted from the boat during their first date. He was given an additional six months for absconding, having fled to Georgia several months before his trial.
When questioned as a witness by police the day after the tragedy, Shepherd admitted he was the "most drunk" he had ever been while at the wheel, having downed a double vodka, wine and champagne.
But he argued at the Court of Appeal that his manslaughter conviction should be overturned because he was not given legal advice ahead of the interview.
The web designer told officers he drank “very heavily” before allowing Miss Brown to take control of his boat.
He said he was so drunk, his memory was “hazy” and that on a scale of one to ten, one being sober and ten “paralytic”, he was an eight.
He revealed that despite having taken around ten other women on the boat previously, he had never been that drunk.
Stephen Vullo QC, defending, argued that Shepherd, appearing via video link from HMP Woodhill near Milton Keynes, should have been cautioned when interviewed because the police knew he was being asked about - and admitting to - offences relating to alcohol and speeding on the river.
“He was not not cautioned or offered his right to a solicitor,” he said.
“(The interview) had the shape, form and feel of an interrogation.”
Shepherd’s references to being drunk were largely withheld from the jury yet Mr Vullo admitted that had he been present at his trial, his account of events would have been “much the same” as that given to police.
Aftab Jafferjee QC, prosecuting, insisted that the safety of Shepherd's conviction was "not in any sense imperilled”, not least because Miss Brown was at the wheel when the boat overturned.
He told the court: "The interview was to establish the clear facts of the incident and he was the only individual who could say what happened.
"What he was giving was a narrative. His drinking did not cause the boat to overturn and did not cause her death.”
He said the evidence regarding the amount of alcohol consumed was “available in abundance elsewhere” and argued that any error made by police was of the most “benign the court would come across”.
Shepherd, who was jailed for an additional four years last week for hitting a barman across the head with a vodka bottle the day before he fled the country, is also appealing against the six month sentence he received for absconding.
His lawyers argued that when he was extradited it was not made clear that the Georgian authorities consented to him being prosecuted under the Bail Act.
After listening to several hours of legal argument, Sir Brian Leveson, presiding over the bench in his last criminal appeal before retirement, acknowledged the ongoing pain Miss Brown’ family were being forced to endure.
In a rare personal statement, he said: “For the family of this young lady it must have been a distressing period listening to what is a comparatively clinical analysis of the law. We are very conscious of the loss they have suffered and nothing we have said is intended to detract from their loss.
“We must focus on these arguments and deal with them as the law requires. The fact that we have not dwelled upon the terrible tragedy that took place that day does not mean we are not extremely conscious of it and we extend our sympathies to you.”
Graham Brown, Miss Brown’s father, said after the hearing: "I thought (Sir Brian) Leveson was very kind and I am very grateful for his comments, because we have had a traumatic experience.”
Judgement was withheld until next week.