What was at first consensual sex while tied to the front seat of a car, morphed into a frightening encounter when a combat knife was placed on the woman's chest, and her mouth was held open with metal hooks.

Jonathan Elliott McKeown believed the complainant was consenting to all of the sexual activity that night in his car beside a Nelson river.

But he was found to have crossed the line in his belief that the victim consented to being penetrated with a whip handle.

McKeown has avoided prison on charges for which he was sentenced in the Nelson District Court today; one for sexual violation and the other for his "minimal part" in a drug dealing operation.

Jonathan McKeown's defence that his offending was linked to a brain injury didn't wash with the Crown in the Nelson District Court today. Photo / Tracy Neal

He was instead sentenced to six months' home detention, factoring in the year he has spent on electronic bail and a month in custody.

McKeown blaming his offending on a brain injury didn't wash with the Crown.

Prosecutor Jackson Webber said McKeown had tried to make out that it "wasn't really him" but his brain injury, which he suffered after falling off a roof while doing a handstand.

"There were prior warnings, and he was clearly well into drug consumption," Webber said, including that it was no fall from grace for the 37-year-old – he had not been in a state of grace beforehand.

Defence lawyer Michael Vesty argued the brain injury was the catalyst for "many bad decisions that followed", and that McKeown was using methamphetamine as a rehabilitation aid.

Late one night in May last year, McKeown went to an address in central Nelson, where the complainant, who was unknown to him, had arrived before him.

She had gone with an associate to buy recreational drugs but McKeown instead offered her methamphetamine.

They socialised and consumed meth for a time afterwards, until McKeown offered the complainant a ride home.

He told her he knew about a good place to watch the sunrise. They drove to a secluded location in a valley south of Nelson, near a river.

The complainant said in the summary of facts she expected sexual activity to take place there and was okay with that. While driving there they showed each other short videos on their cell phones containing sexual content.

McKeown spoke to her about writing erotic fiction and commented about rape fantasies.

On arrival they smoked more methamphetamine and sat talking in his car.

He then used a climbing rope that he got from the rear of his vehicle and tied the complainant to the front passenger seat, before engaging in what was described as rough but consensual sex.

At one point the woman pulled her hand out of the rope, but McKeown re-tied it, and then placed a combat knife on her chest.

She then had the rope tied across her neck, and had small metal hooks placed in her mouth to hold it open.

The woman got her hands free again, then McKeown wrapped duct tape over her upper body. He provided more methamphetamine by holding a pipe to her mouth and lighting the meth.

During the encounter she grew scared, but was afraid to tell McKeown to stop, thinking it was safer to go along with the sexual activity.

She later told police that it was for this reason she did not tell McKeown to stop. Towards the end of the encounter the woman was penetrated with a whip handle, which she had not agreed to.

"It is accepted that the defendant believed the complainant was consenting to all of the sexual activity, but his belief in her consent to being anally penetrated with the whip handle was unreasonable," the police summary said.

The two of them smoked more methamphetamine before driving back to Richmond, where McKeown went into Gun City and spent about an hour buying a variety of handheld weapons, while the complainant waited outside.

They then went to a nearby restaurant to play on the pokie machines, buy drinks and consume more methamphetamine.

McKeown supplied two bags of methamphetamine to a group which was the target of a police operation known as Operation Highland. Photo / 123RF

Around 6pm the complainant made an excuse to leave the restaurant and called a taxi. A later medical exam revealed injuries to her neck, arms, hands, chest and thighs and genital area.

A month earlier McKeown supplied two bags of methamphetamine to a group that was the target of a police operation known as Operation Highland, which led to a charge of possession of methamphetamine for supply.

Also in April and May 2021, McKeown took part in communication over the sale price and transaction of small amounts of meth.

On April 9 last year, an associate contacted McKeown looking for a $50 bag of cannabis and the two arranged to meet.

McKeown was arrested on May 31 last year, after police found him near his car parked at Tahunanui Beach in Nelson.

Before he was arrested he tossed a satchel he was carrying into nearby scrub.

The satchel was found by a member of the public who handed it to the police. Inside they found a set of electronic scales, a number of small unused zip-lock plastic bags, four rounds of .44 calibre magnum firearm rounds and 40 .223 calibre rifle rounds.

The Crown acknowledged the rehabilitation and counselling steps McKeown had taken, but the sexual violation was "incredibly traumatic and violent". Webber said while the facts were somewhat unusual, they weren't the result of any brain injury but McKeown's interest in bondage and erotica.

Michael Vesty said McKeown had lost a lot as a result of his meth use, including money from the sale of his house which had "gone up in smoke".

Defence lawyer Michael Vesty. Photo / Supplied

He had lost standing in industries he had worked in, and had damaged relationships with friends and family - some of whom were in court today to support him.

"These are first convictions. This represented a serious spate of offending over a reasonably short period of time."

Vesty said McKeown's month in custody last August was the "best thing that could have happened to him", as it had acted as a circuit breaker in his meth habit.

He said McKeown had since made progress, including engaging with rehabilitation agencies including the brain injury association, and had shown insight into the impact on the victim.

Judge David Ruth said a pre-sentence report had revealed a lot about McKeown, but he was also troubled by a passage in the report which showed the brain injury suffered by McKeown had no bearing on his sexual offending – it was more likely to have been a destabiliser on his mental health, which he'd struggled to cope with.

Meth had then been a disinhibiting factor.

He said McKeown had accepted he needed help, but he also needed to keep getting that help.

Judge Ruth awarded McKeown credits for an earlier guilty plea to the charges. A 16-month prison term was converted to six months' home detention, with the various terms of three and six months home detention on all charges to be served concurrently.

- Tracy Neal - Open Justice, NZ Herald