A shortage of doctors forced the night-time closure of an accident and emergency unit at the Downe Hospital, the High Court has heard.
A judge was told services would have remained unchanged if enough middle-grade practitioners were available to staff the department round the clock.
Campaigners are seeking to reverse the Health Minister's decision to have GPs provide out-of-hours cover at the £64m hospital in Downpatrick.
Judicial review proceedings have been brought by pensioner John Duggan, backed by Down District Council.
They argue it is irrational to undertake such a change just over a year after the hospital opened in 2009.
It has also been claimed that the Department of Health recognised 24-hour emergency services were needed for the local rural population, and that the night-time closure decision involved an element of predetermination.
Since April, GPs have been staffing shifts between 10pm and 8am.
The decision taken by the South Eastern Trust and approved by the minister earlier this year was said to be necessary because of a shortage of middle-grade doctors.
Counsel for the Department yesterday detailed the staffing levels assessed as necessary to properly run the unit.
Eleven middle-grade doctors, not including consultants and associate specialists, would cover the rota without using locums, the court heard.
Barrister Paul McLaughlin said the Trust began to realise a 24-hour service was unsustainable when only five such doctors were available.
Asked by Mr Justice Treacy if the A&E department would have continued as envisaged if the staffing problem had not arisen, the barrister replied: “Absolutely. Quite simply the staff just don't exist. That is the case right across the UK and it isn't actually challenged by the applicant.”
He confirmed that the steps would not have been taken but for the regional shortage.
“These changes wouldn't have been made. That's the Trust's position.”
The hearing continues.