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

Letby, 33, murdered the five baby boys and two baby girls at the neonatal unit of Countess of Chester hospital in northern England where she was working in 2015 and 2016, 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."

(Reporting by Michael Holden, Editing by Kylie MacLellan)