A man stabbed his 86-year-old mother with an ornamental sword then decapitated her and put her head in the freezer, a court has heard.
Philip Tarver, 47, allegedly attacked Angela Tarver and threatened to kill his 83-year-old father Colin at the family home in Woking, Surrey, on December 19 last year.
Opening his murder trial at the Old Bailey, Alexandra Healy QC said: "It is the prosecution case that at around midday that day, in the kitchen of the address, the defendant stabbed his mother in the chest with an ornamental sword, killing her.
"It appears that, whilst the police were making their way to the address, the defendant decapitated his mother, placing her head into the freezer in the kitchen.
"And he amputated her left ring finger, which he placed into a kettle."
When armed police arrived, Tarver - wearing a woman's floral nightie - came to the front door waving a Union flag and holding a knife, saying: "I surrender, I surrender," jurors heard
Ms Healy said Tarver had lived with his elderly and vulnerable parents all his life.
The night before the killing, he had bought six cans of beer and a small bottle of vodka, jurors heard.
In the morning, he allegedly claimed to his father they had been "poisoned" and went about unplugging the phone and computer, saying he was "spring cleaning".
When his father went to speak to him about why the television was also disconnected, the defendant allegedly slammed the door and told him to "go and die".
While he was in the lounge reconnecting leads, Colin Tarver heard a scream and ran into the kitchen, jurors heard.
He found his wife lying on her back and her son holding a sword, the court heard.
The defendant allegedly had a demented look in his eye as he told his father: "I am going to kill you."
He said he had been told to do it by a "supreme commander" or "supreme leader", the prosecutor said.
Colin Tarver grappled the sword out of his son's hands and went outside to call the police.
Having detained the defendant, officers found Mrs Tarver's body on the floor of the kitchen.
Her head was found in a freezer compartment and her amputated ring finger was inside a kettle placed on top of an Angry Birds box next to the body, jurors were told.
Following his arrest, Tarver heard his father was being spoken to by police and allegedly said: "Oh, of course, his wife. His wife is in the freezer."
On arrival at the police station he said he was "sorry for killing her" adding that he "must repent my sins", the court heard.
During a mental health assessment, Tarver explained how he killed his mother, jurors were told.
He was taken to a mental health hospital where he remained until March when he was deemed fit to be interviewed by police.
Tarver denies murdering his mother and making a threat to kill his father.
Ms Healy said the defendant was understood to deny killing his mother.
If jurors reject his assertion, the issue in the case was whether he suffered a psychotic episode triggered by drugs.
Ms Healy added: "If, however, the defence satisfy you, on the balance of probabilities, that it was not drug-induced but was an independent psychotic disorder, which coincidentally developed against a background of cocaine and cannabis use, then that... could amount to a defence that reduces the offence of murder to one of manslaughter."
