Officials said on Friday that Lucy Letby applied to appeal against her conviction last month for killing five baby boys and two baby girls.

Letby killed the infants at the neonatal unit of Countess of Chester Hospital in northwestern England over 13 months from June 2015, injecting them with insulin or air or force-feeding them milk.

The 33-year-old was sentenced at Manchester Crown Court to life in prison with no chance of release.

Judge James Goss, who imposed a rare “whole-life order” on Letby, said she acted with “malevolence bordering on sadism”.

Only three other women have received such a harsh sentence in the United Kingdom.

She was also found guilty of seven murder attempts involving six other babies there but was cleared of two additional charges of attempted murder. The jury was unable to reach a verdict on several other charges.

Letby consistently denied all the charges.

She filed an application for leave to appeal against her conviction at London’s Court of Appeal, a court spokesperson said. No date for any appeal has been set, they added.

Applications for permission to appeal against a lower crown court decision are typically considered by a judge without a hearing.

If this is refused, permission can still be sought at a full court hearing before two or three judges.

The nurse’s conviction, following a harrowing 10-month trial, made Letby Britain’s worst serial child killer in modern history, local media said.

Letby refused to appear in court for her sentencing or to face an outpouring of anger and anguish from grieving parents.

Shortly after, Britain announced plans to give judges new powers to force criminals to attend their sentencing, following a furore over several other high-profile cases where killers refused to appear in the dock.

The government has also launched a public inquiry into the case, which will look at the circumstances of Letby’s crimes and consider accusations from doctors in the neonatal unit that their concerns about Letby were not heeded by senior staff.