LONDON • A teenage couple believed to be Britain's youngest double murderers have been named after a court ruling in London.

Fourteen-year-old Kim Edwards plotted with boyfriend Lucas Markham, also 14, to kill her mother Elizabeth Edwards, 49, and little sister Katie, 13, in April 2015.

The teenagers were jailed for murder for a minimum of 20 years each last November but could not be named for legal reasons.

Judges at the Court of Appeal lifted the ban last Friday after a lengthy court battle, meaning the full details of the case can be revealed for the first time.

The couple, who were described as being in a Bonnie and Clyde-like relationship, had planned the murders days before. Kim reportedly had a falling out with her mother and sister over her new boyfriend, said The Telegraph.

Mrs Edwards was concerned that Lucas, who had been expelled from school, was becoming a bad influence on her daughter.

Jurors were told that Kim's grudge against her mother was so intense that she had fantasised about killing her for some time, and she was also jealous about the love and attention received by her younger sister.

During the trial, the court heard how Lucas had inflicted the fatal knife wounds, but Kim had been just as guilty in carrying out the "cold, calculated and callous killings". Prosecutors said Mrs Edwards and Katie were stabbed a total of 10 times.

For the next 36 hours after the killings, the couple remained downstairs in the house in Spalding, Lincolnshire, while the bodies were upstairs. They shared a bath, had sex and watched four vampire-themed Twilight films while eating ice cream and tea cakes, the court was told.

Police said the couple "showed no remorse at all when they were eventually found by officers and during their police interviews".

On appeal, the sentences were reduced by the judges last Friday to 171/2 years each, reported The Guardian.