The British banker accused of murdering two Indonesian women in his upscale Hong Kong apartment is a narcissistic sexual sadist who had been abused at school, a court heard Monday.

Rurik Jutting, a 31-year-old Cambridge graduate, has pleaded not guilty to murder but guilty to manslaughter on the grounds of diminished responsibility. The prosecution rejected the lesser plea.

Jutting is accused of murdering Sumarti Ningsih, 23, and Seneng Mujiasih, 26, two years ago, slashing their throats after saying he would pay them for sex.

He tortured Ningsih inside his apartment for three days before killing her and stuffing her body in a suitcase found on his balcony.

As the trial entered its second week, the defence said Jutting suffered from narcissistic personality disorder and sexual sadism disorder, as well as heavy use of cocaine and alcohol.

He had also experienced bouts of depression and suicidal thoughts, the court heard.

Forensic psychiatrist Richard Latham, called as a defence witness, said Jutting had told him he was abused at renowned English private school Winchester College.

A report from Latham read out in court said a boy had forced Jutting to perform oral sex on him at school.

‘He described it in a way that he was a victim of sexual assault,’ Latham said.

Latham said people with narcissistic personality disorder had problems empathising with others and sought constant praise.

‘When that breaks down the consequence is dramatic,’ Latham told the court.

Latham also said Jutting had described how he had become increasingly interested in torture, ‘culminating in dramatic and horrific acts’.

His disorders mixed with the consumption of cocaine and alcohol had affected his behaviour, said Latham.

‘At the time of the killings his ability to control his behaviour was substantially impaired,’ the psychiatrist said.

When asked by judge Michael Stuart-Moore whether voluntary intoxication constituted a defence, Latham said the drive to take drugs and alcohol was ‘extremely difficult to resist’.

- 'Complete blackout' -

The court heard how Jutting had been unhappy at work in London and by 2012 was drinking heavily, consuming 84 units of alcohol a week -- the equivalent of 14 bottles of wine.

He sought therapy at that time and had previously seen a psychiatrist at school, when he was worried about his parents' marital problems.

Arriving in Hong Kong to work for Bank of America-Merrill Lynch in 2013, he continued drinking and spent his spare time watching television and playing computer games, according to a report by Latham read out to the court by defence counsel Tim Owen.

Jutting had no social life and the point of drinking was to ‘achieve complete blackout’, Latham's report said.

The court heard that Jutting had periods of depression and had considered suicide before the killings. In 2014 he was bingeing on takeaway food and had amassed debts, Latham said in his report.

Ningsih and Mujiasih were found dead in Jutting's flat in the early hours of November 1, 2014.

In police interviews shown to the court last week, Jutting told officers he had been taking 10 grams of cocaine a day in the weeks before the killings.

Owen said Jutting had been introduced to cocaine by escorts in London in 2010 and that in 2011 he had gone on three-day binges, taking five grams of cocaine at a time.

‘I think five grams is a lot of cocaine for a person to take, suggesting that there was some tolerance at that stage,’ Latham said.

Defence arguments were continuing Monday afternoon.