A man convicted of killing a woman in a speedboat crash on the Thames will remain in custody in Georgia for three months pending extradition proceedings.

Appearing at Tbilisi city court on Friday, Jack Shepherd, 31, said he was “suicidally depressed” and his decision to go on a speedboat date with Charlotte Brown, 24, was his “greatest regret”.

Shepherd, originally from Exeter, surrendered to police in Georgia on Wednesday, six months after failing to attend his trial at the Old Bailey. He was sentenced in his absence in July to six years in prison for the manslaughter by gross negligence of Brown.

On Wednesday, he gave an interview claiming his innocence over her death.

Shepherd and Brown met on the dating website OkCupid and were on their first date when they were involved in a speedboat crash on 8 December 2015. He had taken her for a meal at the Shard in London before suggesting they go for a late-night boat ride past the Houses of Parliament.

The boat hit a submerged log near Wandsworth Bridge and capsized, flinging Brown into the river. Shepherd was rescued after being found clinging to the upturned hull. Brown was found unconscious and unresponsive. A postmortem ruled she died from cold water immersion.

During the hearing on Friday, he told the court: “Not a single day passes when I don’t think about the loss of Charlotte’s life and the effect this has had on her family. Some time after the accident, I felt suicidally depressed at what had happened. That’s why I’ve been unable to speak about it.”

Shepherd, who has been working in Georgia, said he wished he had sat down with Brown’s family and explained what happened. “I can see that not to have done so has caused them great pain and suffering,” he said. “I’m very sorry for that and that’s why I handed myself in now just to draw to a close this horrible accident and all the terrible consequences.”

One of his defence lawyers said Shepherd should not be extradited because he had been warned in a phone call that his life might be in danger if he went to a UK jail. The court also heard Shepherd had an alcohol dependency and wanted to conduct an appeal against his conviction from Georgia.

Play Video 0:27 Georgian TV films moment man who killed woman in speedboat crash hands himself in – video

Speaking before the court appearance, Tariel Kakabadze, Shepherd’s lawyer in Georgia, said his client may still fight his extradition to the UK, where his legal team have been granted leave to appeal against his conviction. “It’s Jack Shepherd’s decision not to fight for release on today’s court session,” he said.

The Crown Prosecution Service is responsible for submitting an extradition request through the Home Office. It is then down to Georgian authorities to manage the process, with no time restrictions on how long it should take.

A CPS spokesperson said: “The CPS is doing everything it can to help make sure Jack Shepherd faces justice through the proper legal channels. Extradition is a complex process and we are continuing to work with UK colleagues and the authorities in Georgia to progress it as quickly as possible.”

The UK has an extradition agreement with Georgia. Under Georgian law, Shepherd can be detained for up to nine months before extradition. Prosecutors are required to apply for restriction measures for a person wanted in another country within 48 hours of them being arrested.

Theresa May’s spokesman said the prime minister “welcomes the news that [Shepherd] is now in custody”. He added: “The government will now work alongside the police and the Crown Prosecution Service to ensure that extradition proceedings are expedited.”

It was reported in the Mirror that while in Tbilisi, Shepherd had rented a flat and been a regular at a local bar, as well as going on ski trips.

Commenting on the story on Facebook on Friday, Charlotte Brown’s sister Katie said: “This is unbelievable. Jack Shepherd on a 10-month holiday whilst we had to sit through a trial to try and make sense of what happened to our Charli. Where is this man’s dignity and remorse?

“From what I’ve seen, I don’t believe he will reflect and learn from his actions in this lifetime. The main person he is hurting now is himself … Don’t think you’ll be skiing or going to nightclubs anytime soon Mr Shepherd.”