A retired accountant has been jailed for a minimum of 18 years after being convicted of the murder of her husband, a former army lieutenant colonel.

Penelope Jackson, 66, was found guilty at Bristol crown court of the murder of David Jackson, 78, whom she stabbed three times at their home in Berrow, Somerset, on 13 February.

Imposing a life sentence with an 18-year minimum term, the judge Martin Picton said: “I have no doubt you intended to kill your husband and it was a pre-meditated murder. Your behaviour shows a shocking level of callousness. During the four days of giving evidence I did not detect a shred of genuine remorse on your part for the crime you have committed.”

He said he had given a higher sentence than the 15-year minimum outlined in sentencing guidance owing to the physical harm inflicted on David Jackson.

During the high-profile two-week trial, the defence lawyer, Clare Wade QC, sought to persuade the jury that Penelope Jackson had a “loss of control” after being pushed to the edge by decades of intermittent emotional and physical abuse.

However, the jury decided that despite the legacy of abuse, Jackson was in control of her actions on the evening when she stabbed her husband three times, and that her behaviour was not consistent with that of a person with a “normal degree of tolerance and self-restraint”.

Picton said: “There were no doubt tensions in the marriage, points of friction the lockdown will have accentuated, but I’m quite sure he was nothing like the person you claimed.”

Jackson killed her husband after sharing a birthday meal with him and with their daughter via Zoom. The couple had rowed over a bubble and squeak side dish, and then over the location of an iPad charger, before Jackson retreated to the main bedroom carrying a kitchen knife. She told the jury she had planned to use it for self-defence, and later considered suicide.

Jackson said she entered her husband’s bedroom seeking an apology for the events of the evening. When he failed to say sorry, she said, she informed him of her intention to take her own life. She said he goaded her, suggesting she “get on with it”.

Jackson told the court this was the moment when she “lost it”. She said: “I just thought: I cannot do this. It is not fair and I lost control.”

Jackson stabbed him across the chest in the bedroom, and said she then went downstairs to write a note of confession. Her husband emerged later to call 999, and during the course of that phone call – in which she reported him telling her that she “couldn’t even do [the stabbing] right”, she fatally stabbed him two further times in the abdomen.

In an 18-minute phone call to emergency services, Jackson told the call handler that her husband was “bleeding to death with any luck” on their kitchen floor. She repeatedly refused to help the victim when the operator asked her to take steps such as apply pressure to the wound or throw him a towel to try to stem the bleeding.

Jackson confessed in the 999 call to killing her husband and claimed she was “compos mentis”, but in a later statement she said she remembered little of the evening’s events and had been in a state of traumatised shock.