A British banker serving a life sentence for killing two Indonesian women in Hong Kong after subjecting them to three days of alcohol- and cocaine-fuelled torture and rape will appeal against his conviction, his lawyer has said.

In November 2016, Rurik Jutting, 31, a Cambridge-educated employee at Bank of America Merrill Lynch, was unanimously convicted of the murders in 2014 of Indonesian immigrants Sumarti Ningsih, 23, and Seneng Mujiasih, 29.

The appeal will focus on “the directions given to the jury by the deputy judge”, said Michael Vidler, one of Jutting’s lawyers. Arguments will be presented on 12 December at Hong Kong’s court of appeal.

He is serving his sentence at the maximum security Stanley prison, a colonial-era jail on the southern coast of Hong Kong island.

At the time of his conviction, Jutting said he accepted the court’s ruling so the decision to appeal comes as a surprise. “The jury has delivered a verdict that I cannot and do not have any objection to,” he said in a statement read by his lawyer.

He had claimed diminished responsibility for the killings, which he filmed on his iPhone, at one point saying: “I don’t really feel guilty.”

Tim Owen QC, the British lawyer that defended Jutting, had argued his client suffered from a personality disorder and should be found guilty of the lesser charge of manslaughter. That charge is typically punished with a fixed prison term, although a judge could still sentence Jutting to life behind bars.

At the time of sentencing, Judge Michael Stuart-Moore said: “During this trial we have been made to dredge the very depths of depravity during the three days of torture he subjected his first victim to.

“He described himself as evil and a monster, and neither is adequate to describe the true nature of what happened. The defendant is the archetypal sexual predator.”