Nurse Lucy Letby, Britain's most prolific serial child killer in modern times, will spend the rest of her life behind bars for murdering seven newborn babies and trying to kill another six, a judge ordered on Monday.

Letby, 33, murdered the five baby boys and two baby girls at the neonatal unit of Countess of Chester hospital in northern England over 13 months from 2015, injecting the infants with insulin or air or force feeding them milk.

Some of those she attacked were twins – in one case she murdered both siblings, in another she killed two of three triplets, and in two instances she murdered one twin but failed in her attempts to kill the other.

"This was a cruel, calculated and cynical campaign of child murder involving the smallest and most vulnerable of children," said the judge, James Goss, who sentenced her to life imprisonment with no prospect of release.

"There was a deep malevolence bordering on sadism in your actions ... You have no remorse. There are no mitigating factors ... You will spend the rest of your life in prison."

Whole life orders are very rare, and only three women in Britain have received such a sentence before, including serial killers Myra Hindley and Rosemary West.

Letby refused to leave the cells to hear her sentence being handed down, leading to demands that criminals must be forced to hear the impact on their actions on their victims or their families. The mother of one of the victims described it as a final act of wickedness.

The harrowing crimes committed by Letby, who was in her 20s when she carried out her killing spree, have horrified Britain, and wrecked the lives of victims' families and had a lasting damaging impact on her colleagues.

She was found guilty last week of seven counts of murder and seven of attempted murder following a 10-month trial at Manchester Crown Court. Jurors were unable to agree on whether she had tried to kill six and acquitted her of two other charges of attempted murder.

Earlier the court heard emotional, heart-wrenching statements from the parents of those she murdered and tried to kill, recounting the horror and trauma of losing their babies.

"There is no sentence that will ever compare to the excruciating agony that we have suffered as a consequence of your actions," said the mother of one baby boy she murdered. (Reuters)