An acclaimed British crocodile expert who worked with Sir David Attenborough has pleaded guilty to dozens of charges of bestiality involving the torture, sexual assault and killing of more than 40 pet dogs.

Adam Britton moved from the UK to the Northern Territory of Australia as a young man to pursue his interest in saltwater crocodiles, the giant predators that live across the tropical regions of the country.

Based in Darwin, the zoologist wrote books, collaborated on films, made nature documentaries with the BBC and National Geographic and kept a pet half-tonne, 16-foot-long saltwater crocodile, which he named Smaug.

But on Monday, the 51-year-old pleaded guilty in the Northern Territory’s Supreme Court to 60 criminal charges ranging from animal cruelty to raping or attempting to rape a dog and possessing and transmitting child abuse material.

The details of the charges were so horrific that the judge, Chief Justice Michael Grant, warned people in the court that the evidence could cause “nervous shock”.

In an unusual move, he gave people in the public gallery, journalists and security officers the option of leaving the courtroom.

Britton had committed “acts that could only be described as grotesque cruelty which are both confronting and distressing. In my assessment (they) have the potential to cause nervous shock or some other adverse psychological reaction to a person exposed to those details,” the judge said. “Either way I’ll leave that up to you, but the potential has been described.”

The wildlife worker, who is originally from West Yorkshire, was arrested in April last year. A suppression order had hidden his identity but it has now been lifted.

The court heard that he had a “sadistic sexual interest” in animals, in particular dogs, and that he had intentionally killed around 40 animals in a pattern of behaviour that dated back to 2014 at least.

The court heard that Britton, who was married for 15 years and who completed his PhD in zoology at the University of Bristol, had a shipping container on his property that he called his “torture room”.

When police raided the rural property near Darwin last year they found the container was packed with computers, cameras, external hard drives and sex toys.

Prosecutors said Britton used the container “to torture, sexually exploit and kill dogs”.

He acquired the pets through Gumtree Australia, an online marketplace, assuring their former owners that they would be well looked after.

“[He] often built a rapport with the dog owners in negotiating taking custody of their animals, many of whom had to reluctantly give their pets away due to travel or work commitments,” said Crown prosecutor Marty Aust.

Police officers also found several files of child abuse material on Britton’s laptop.

Mr Aust said that the accused had a Telegram account which he used as a means of contacting “like-minded people”. 

He had another account with which he uploaded and disseminated video recordings of him torturing and sexually abusing dogs. He is accused of sexually abusing his own pet dogs, two Swiss Shepherds called Bolt and Ursa.

One such video was passed to an animal welfare organisation, which referred it to police.

“Using these applications, the offender discussed his ‘kill count’ … and described the shipping container on his property as his ‘torture room’,” Mr Aust said.

In an online message which was read out in court, Britton wrote to a contact: “I had repressed it. In the last few years, I let it out again, and now I can’t stop. I don’t want to.”

Britton was for many years a respected academic at Charles Darwin University in Darwin.

A few years ago his pet crocodile Smaug featured in Life in Cold Blood, a BBC wildlife documentary narrated by Sir David Attenborough.

“They really wanted to get a shot of two crocodiles copulating underwater. I said: ‘OK, whatever you want [but] it will be virtually impossible to film in the wild’,” he told the Australian Broadcasting Corporation in 2015.

Britton said he has also collaborated with Bear Grylls. “He was a bit of a sook (Australian slang for wimp) to be honest. He was definitely a bit apprehensive about going in with Smaug,” he told the ABC.

Britton was remanded in custody. The case was adjourned for sentencing in December when it is expected defence lawyers will make submissions.