A 16-year-old boy “lost his temper” and fatally stabbed a woman after she inhaled laughing gas last Christmas Eve, a court has heard.

Kacey Clarke, 22, was allegedly stabbed in the chest by the youth during a row in a flat in Bermondsey, south-east London.

Shortly before, the boy had been caught on CCTV audio threatening to “ching” her up, saying: “I’m going to kill you,” jurors heard.

Like the alleged victim, the boy was said to have a history of inhaling nitrous oxide – commonly known as laughing gas.

A search of his bedroom revealed a large collection of cannisters, the Old Bailey was told.

After the killing, it is alleged that the youth hid the murder weapon – a large knife – in a railway arch where it was later discovered by a Thames Water workman.

Opening his trial on Tuesday, Jane Osborne KC said the defendant had “lost his temper” with mother-of-one, Ms Clarke.

The prosecutor said: “They might have been arguing, they might even have been fighting, but that argument met a fatal end when (the defendant) armed himself with a very large knife … and used it to stab (Ms Clarke).

“His intention to stab … is nowhere more evident than on the audio footage which records him shouting that he is going to ‘ching’ her up and kill her.”

Earlier, Ms Clarke had texted a relative, who got the impression she had been inhaling intoxicating substances, jurors heard.

Ms Clarke told the relative that she had been taking “balloons”, which was slang for inhaling nitrous oxide, Ms Osborne said.

When challenged about it, Ms Clarke allegedly told her relative she “shouldn’t be boring because it was Christmas”.

Another relative, texted to say Ms Clarke was “buzzin like nothing”, the court was told.

Police and paramedics were called just after 10pm and found Ms Clarke was lying on the kitchen floor of the Bermondsey flat with a single stab wound to the chest.

The defendant was arrested nearby around 45 minutes later.

He had been wearing Croc shoes and blood was found on his bare toe, jurors were told.

Clumps of his hair that appeared to have been ripped from the scalp were also recovered from the scene, the court heard.

A broken lamp and picture frame were found on the floor of the living room as well as a bag of the clothes believed to belong to the victim beside two large 640g nitrous oxide cannisters, jurors were told.

In a police interview, the defendant offered a prepared statement in which he said Ms Clarke had become angry that she could not find her car keys.

She smashed a lamp and threw something at the defendant, hitting him on the side of the face, he said.

A fight ensued with Ms Clarke grabbing his hair, he claimed.

Ms Clarke then burst into a room holding a knife and the boy said he picked up a blade and waved it to create an “invisible shield”.

He said he thought she was lying when she said she had been stabbed as he had no recollection of making contact, according to the statement.

Ms Osborne asserted that the defendant intended to harm to Ms Clarke and hid the knife in the railway arches to “cover his tracks”.

She suggested that an attempt to say he had no idea that he had stabbed Ms Clarke was “almost certainly a lie”.

The defendant, who cannot be identified because of his age, has claimed he acted in self-defence.

He denies murder and an alternative charge of manslaughter.

The Old Bailey trial continues.