A British man was handed a life sentence Thursday, after his partner died from injuries caused 21 years earlier when he doused her in petrol and set her on fire.

A judge at Bristol Crown Court in western England told Steven Craig he would have to serve a minimum of 15 years in prison for murdering Jacqueline Kirk.

Craig, 58, had already served more than 15 years behind bars for grievous bodily harm with intent for the attack in nearby Weston-super-Mare in 1998.

But following Kirk's death in 2019 aged 61, he was charged with her murder two years later and then convicted unanimously by a jury last month.

The court was told that the injuries he had caused -- including burns to 35 percent of her body -- played a part in her dying from a ruptured diaphragm more than two decades on.

Kirk, a mother of two who spent nine months in hospital and required 14 operations including a tracheotomy and skin grafts following the attack, surprised doctors by surviving so long.

Aged 41 at the time of the attack, she lived to see both of her children get married and became a grandmother.

"That was a really really important thing for all of us, to have our mum for those life events," her daughter told Sky News.

"We were told she probably wouldn't survive after 10 years, so we made the most of it."

In August 2019, Kirk was taken to hospital with a swollen abdomen and died the next day.

During Craig's murder trial, jurors were persuaded that scarring to her chest and abdomen complicated doctors' efforts to treat her for intestinal swelling.

Craig, of York in northern England, admitted the 1998 attack but denied being responsible for her death.

"It is an unusual case, purely for the amount of time that's passed," Detective Chief Inspector Mark Almond, of Avon and Somerset Police, told Sky News.

"It's been really important for us to find the right medical experts to comment on the case and give us the evidence we needed to present to that jury."