The first signs something was wrong at the Countess of Chester Hospital ’s neonatal unit emerged in July 2016.

That’s when it was announced the most poorly babies would be looked after at Arrowe Park Hospital or another neighbouring unit in future.

What was described as a ‘temporary measure’ only related to infants with high dependency needs, affecting one or two babies out of around 60 births during an average week.

The step was taken because the Countess wanted to understand why there had been a greater number of deaths than it would normally expect on its neonatal unit between January 2015 and July 2016.

The Countess then commissioned an independent review by the Royal College of Paediatrics and Child Health and The Royal College of Nursing which found ‘significant gaps in both medical and nursing rotas’.

Staffing levels were sufficient for a level 1 Special Care Baby Unit but not for a level 2 Local Neonatal Unit – the former status of the Countess unit – providing longer term high dependency and some intensive care.

The review also found arrangements for investigating neonatal deaths ‘must be strengthened’.

Among the 24 recommendations were the need to review each unexpected neonatal death in the relevant period, strengthen the response to neo-natal death/near-miss investigations, to appoint two additional consultants, ensure the maintenance of skills of neonatal nursing and medical staff and to create a ‘children’s champion’ on the hospital board.

Ian Harvey, medical director at the Countess of Chester Hospital

Medical director Ian Harvey confirmed at the time the hospital had ‘acted swiftly’ to review case notes in relation to 13 unexplained deaths.

But the hospital must have been concerned it had not got to the bottom of the matter, leading managers to call in Cheshire police who widened the scope of the inquiry to examine the deaths of 15 infants when its investigation launched in May 2017.

In addition, the probe conducted a review of six non-fatal collapses during the same period.

Today Cheshire police revealed a female health professional had been arrested on suspicion of murder in relation to eight babies and attempted murder in relation to six babies. And the inquiry has been widened again.

Detective Inspector Paul Hughes, of Cheshire Police , confirmed: “We are now currently investigating the deaths of 17 babies and 15 non-fatal collapses between the period of March 2015 and July 2016.”

Chief executive of the Countess of Chester Hospital Tony Chambers

Hospital chief executive Tony Chambers told The Chronicle earlier this year about why it was decided to call in police.

He said: “We have had various inquiries including the Royal College of Paediatrics review and there were just a few niggles that our clinicians said, look, we think we have got 90% of the answers but there are still bits that we need to in a sense be clear that we have not missed anything.

“All we know for certain is that for that period of time, against a very, very low mortality rate in West Cheshire, there had been a spike that we couldn’t explain.”