A 15-year-old girl has been found guilty of murdering a woman and her teenage daughter.

Dinner lady Elizabeth Edwards, 49, and daughter Katie, 13, were stabbed through the throat and smothered in their beds at their home in Spalding, Lincolnshire in April.

The girl carried out the killings with her boyfriend - who had already pleaded guilty.

The teenagers, who were both 14 at the time, are thought to be Britain's youngest couple to ever be convicted of murder.

Afterwards they shared a bath, had sex and watched the vampire-themed Twilight films, Nottingham Crown Court heard.

The girl, who cannot be named for legal reasons, had previously admitted manslaughter on the grounds of diminished responsibility but this was rejected by the prosecution.

Jurors heard the pair - described as being in a Bonnie and Clyde-like relationship - had planned the murders days before.

The girl told police it had started off as a joke but escalated into reality as she had "felt like murdering for quite a while".

In interview she said a gun would have been easier but "we don't really have any in this country" - so a knife was a better solution.

She watched her boyfriend kill the woman by knifing her through the voice box to ensure her daughter was not woken by her screams.

Although she did not watch the subsequent killing of Katie, the girl described hearing "moaning" from the younger victim's bedroom as her boyfriend smothered her with a pillow.

The house in Spalding where the victims were killed. Credit: PA

In police interviews and assessments with psychiatrists, the girl described the killings as "a breeze".

And afterwards she said her boyfriend, who also cannot be named, "seemed fine".

She said the pair had planned to kill themselves by taking pills after the murders but changed their minds.

Both killers now face indefinite detention at Her Majesty's pleasure - the juvenile equivalent of a life term for an adult.

Detective Chief Inspector Martin Holvey said the attacks had a "shocking impact" on the community.

He added: "This case has left a number of lives in ruins, not only Elizabeth and Katie's families but also the two juveniles who committed this horrendous crime.

"What makes this case even more shocking is that these two were aged just 14 when they planned and committed these callous, senseless, and unprovoked attacks on Elizabeth and Katie."