Nancy Pexton with her sister Jennifer Abbott

IN the end, the best explanation the Old Bailey jury heard for murder was sibling rivalry, a one-sided jealousy, at least, and a relationship drenched in bubbling resentment.

But as Nancy Pexton, 70, from Marylebone said nothing during her trial for murdering her sister last June, the question where the anger first took root was unanswered.

On Friday Judge Anuja Dhir KC handed down a life sentence, with a minimum tariff of 22 years. Pexton will be in her early 90s before she is eligible to appeal for release.

The court heard that Jennifer Abbott, 69 – just nine months her junior – had been stabbed several times at her home in Mornington Place.

The dead woman’s son, Brad Carlson, said in a statement read to the sentencing hearing: “Without her in my life it feels like the star in my solar system is gone.

Losing a mother is painful enough but the circumstances in which she died feel like a night­mare which I cannot wake from.”

Those circumstances had shocked everybody living on the estate in the back streets of Camden Town. Pexton had left her sister’s body with tape covering her mouth, while Abbott’s corgi, Prince, was locked away in another room.

Pexton had sent angry messages to her sister and, on a list of reminder notes on her phone, she had written: “I am planning to kill my sister whom I love but she destroyed my life with her mouth. Loose lips can sink ships and she sunk my ship.”

Mr Carlson told an earlier hearing of the tempestuous relationship between the sisters, although it was not said what fuelled the final breakdown. “There was chemistry between them, love at times and at times anger, and resentment,” he said.

“Sometimes they made up, sometimes they went long periods without talking.”

Judge Dhir said the taping of her sister’s mouth was a “deliberate act of degradation”, and added: “It was callous, demeaning, and cruel, this action taken alone demon­strates the depth of your animosity and hostility towards your sister on the day of the killing.”

She told Pexton, who appeared via video- link from prison: “Also before leaving the flat you took your sister’s most prized possession, the Rolex watch given to her by her only child Brad in gratitude for the sacrifices made by her.”

The watch had been a key clue when detectives realised the treasured timepiece was missing.

Ms Abbott, who sometimes went by the name Sarah Steinberg, was discovered when a neighbour broke down the door after he became concerned he could not hear Prince barking. The last time she was seen alive was on a door camera when she took the dog for an early-morning walk. Pexton later spoke to her on the phone and travelled by bus to the flat. She left after an hour and called her GP to say she had taken an over­dose. She was arrested a few days later in a bed at University College Hospital. Police decided last week to release footage of the moment she was arrested on a hospital ward.

During questioning, Pexton was asked why the diamond encrusted watch had been found in her bag and replied: “Oh yes that’s my sister’s. She asked me to look after it”.

Mr Carlson had told the court earlier that he had given it to her as a gift in 2004 to thank her for everything she had done for him. In his statement he added: “She was a single mother raising her only child, committed to providing me with the life she was not lucky enough to have. boarding school, quality education. Most importantly she gave me love and a feeling of belonging and pride. She was my whole world, she was everything to me. What happened to her in the place she should have been safest, in her home, is something I struggle to come to terms with.”