There was "denial, deflection and delay" by hospital bosses to investigate Lucy Letby's crimes at the Countess of Chester Hospital, the Thirlwall Inquiry has heard.

Lawyers representing families of babies born at the Countess of Chester Hospital, during the time the convicted serial killer worked in the neonatal unit, have been giving their opening speeches on Thursday, September 12.

Peter Skelton KC, representing the families of twins Child A and Child B, Child I, twins Child L and Child M, Child N, and Child Q, said "vital information was overlooked with fatal consequences", and the hospital should have investigated what had gone on much sooner.

The inquiry again heard of the parallels to the cases of killer nurses Beverley Allitt – who Letby had learned about during her University of Chester nursing training – and Victorino Chua, who was found guilty in May 2015. Both had used insulin to poison patients.

Mr Skelton said staff at the Countess should have had "heightened awareness" for unexplained events in light of those criminals, and be prepared to "think the unthinkable".

He said there was "denial, deflection and delay" on behalf of the hospital executives, and an "inexplicable failure" to provide information to relevant external bodies.

While praising whistleblower consultants Dr Ravi Jayaram and Dr Stephen Brearey for their "tenacity and courage", Mr Skelton said they should have been more "unambiguous" and made their concerns known formally, in writing – and if managers did not take the appropriate action, they should have gone to the coroner or police.

He noted, for the inquest of Child A, when consultants were under oath, that should have been a moment for them to let the coroner know of the cluster of deaths.

He added, however, the most serious failings were reserved for the managers, Eirian Powell, Alison Kelly and Ian Harvey, who "failed to act with professional curiosity" at the time. Mr Skelton was critical of former medical director Mr Harvey, who in his statement to the inquiry, "simply doesn't accept personal responsibility for the fact Letby was not caught sooner."

Mr Skelton acknowledged the Countess of Chester Hospital Trust had since reflected carefully on the "serious mistakes that were made".

He urged some of the hospital bosses due to give evidence that they should give a "greater level of insight" than that which had been supplied in their written statements to the inquiry, as they had "continued denials and deflections".