Chilling confessions of UK's youngest double killers, Kim Edwards and Lucas Markham, revealed

Lucas Markham and Kim Edwards. (Lincolnshire Police)

The chilling confessions of two teenage killers believed to be Britain’s two youngest double murderers have been revealed, after judges allowed the pair to be identified last week.

Three Court of Appeal judges in London lifted a prohibition banning the identification of Kim Edwards, 15, and her 15-year-old boyfriend Lucas Markham, in the murders of Elizabeth and Katie Edwards, Katie's mother and sister, as they slept at their home in Lincolnshire in April 2016. The two hatched the plan after her mother tried to break them up, according to The Sun.

Investigators said the teens, both 14 at the time of the murders, had sex after the killings, then shared a bath before watching the "Twilight" movies, according to The Sun.

In a portion of the police interview with Kim Edwards released earlier this month, the teen said one of the reasons behind the killing were her mother "favored my sister more than me."

A new documentary to air Monday about the killings called "Murdered By My Daughter" features exclusive access to the confession by Markham.

In the audio obtained by Channel 5, Markham confessed in a calm, undramatic voice, saying “I went into her mum’s room and stabbed her in the neck while she was asleep on her side and smothered her face with a pillow," according to The Sun.

“And after I knew she had gone, I went into Katie’s room – which is the same room as Kim’s – and I thought I stabbed her, but… I thought I stabbed her, but I’m not a hundred per cent sure – it was, like, her on a mattress and then I smothered her face with a pillow too.”

Markham admits killing Elizabeth then says he killed Katie because he thought she would call the police.

Authorities in Lincolnshire have said the newly released information will "undoubtedly focus attention" on the horrific case once again.

“The murders of Elizabeth and Katie Edwards were horrific and brutal and the whole country shared a sense of shock that two juveniles, who were only 14 years old at the time, could have carried out such a horrendous act," Lincolnshire Detective Superintendent Martin Holvey said in a statement.

“I’m sure that sense of disbelief and horror will be deepened now it is known that it was Elizabeth’s own daughter who was responsible for plotting with her boyfriend to carry out the murders."

The teenagers were given a 20 year prison sentence in November.

Read more from The Sun.