Moorfields Eye Hospital. Photograph: Geograph.

Moorfields Eye Hospital has admitted that Brexit poses a significant risk to its planned multi-million pound move to a purpose-built site in King’s Cross.

The relocation of the historic ophthalmological centre represents the biggest NHS project in London, and it is being closely scrutinised by Islington councillors.

The plans are part of a wider scheme within North London in which mental health services at St Pancras Hospital would be moved to the Whittington Hospital, with two acres of land potentially sold to Moorfields for a new eye care, research and education facility.

However, representatives for Moorfields conceded that Brexit could bring the whole plan into question when grilled by councillors at a 7 March meeting of Islington’s health and care scrutiny committee.

Johanna Moss, director of strategy and business development, said: “The sales receipt from the City Road site is a significant part of the funding strategy for the proposed new building, so [a decline in property values resulting from Brexit] is up there on the top of our risk register.

“We’ll be looking at affordability and what impact Brexit has or hasn’t had on the land value.

“There’ll also be detailed financial analysis in our full business case, so we will be testing the land value of the City Road site, and obviously if there are big swings either way there’ll be a point of decision, dependent on that financial position.”

Impact from Brexit on the eye hospital to date was described at the meeting as “minimal”, with managers said to be taking steps to support and protect their EU staff.

Moss described the move as having the potential to be a “huge wrench” given the emotional attachment of both staff and patients to the building, with one of her colleagues recently celebrating her 45th anniversary of employment at Moorfields.

However, a litany of issues with the current site were set out to councillors, as the amount of patients in an aging population grows year on year.

The age of the facilities was said to constrain developments in more effective treatments, and professionals are limited in their ability to interact at the current City Road site, resulting in a lower likelihood of what were described as “magic water-cooler moments” in professional collaboration.

Moss said: “Our current site is not very energy-efficient, because of its age. A purpose-built new facility would be better from a sustainability perspective.

“We shouldn’t underestimate the emotional attachment people have to City Road, and it’s not a decision we’d take lightly to move, as it will have an impact on both staff and patients.

“We did look at whether or not we could rebuild on City Road, and concluded that simply wasn’t affordable because we weren’t generating sales receipts from that.”

Tracy Luckett, director of nursing and allied health professions, added: “We are providing good, 21st-century care in a 200-year-old hospital. It’s very fragmented, and not what you need to give great patient care.”

The relocation is projected to cost £400m, with £110m provided by central government and the rest from the sale of City Road and philanthropic donations.

Moss said: “In the short-term, we probably could stay, but this is about making sure we continue to provide care, research and education through to 2050.

“We all agree that we’re on a slow decline if we don’t move.”