The 1270 sq km berg split off from the Brunt Ice Shelf, where the UK’s Halley research station is based.
The British Antarctic Survey (BAS) confirmed the calving on Friday, saying their research base – which sits inland on the floating ice shelf – is not considered likely to be affected.
The 12 people working at the station – which is closed for the Antartic winter – left in mid-February.
The BAS said the iceberg that broke off from the Brunt Ice Shelf on Friday was the size of Bedfordshire.
It was approaching the size of London, which measures around 1500 sq km.
Simon Garrod, the director of operations at BAS, said it was a “dynamic situation”.
“Four years ago we moved Halley Research Station inland to ensure that it would not be carried away when an iceberg eventually formed. That was a wise decision,” he said.
“Our job now is to keep a close eye on the situation and assess any potential impact of the present calving on the remaining ice shelf”.
The first signs a calving event – where chunks of ice break off from a glacier or ice shelf – was “imminent” appeared last November, when a new chasm called the North Rift on the Brunt Ice Shelf headed towards an existing large one, according to BAS.
“During January, this rift pushed northeast at up to 1km per day, cutting through the 150m thick floating ice shelf,” the research institute said in a statement.
“The iceberg was formed when the crack widened several hundred metres in a few hours on the morning of 26 Feb, releasing it from the rest of floating ice shelf.”
Professor Dame Jane Francis, the director of BAS, said teams had been preparing for an iceberg breaking off for years.
“Over coming weeks or months, the iceberg may move away; or it could run aground and remain close to Brunt Ice Shelf,” she said.
“Halley Station is located inland of all the active chasms, on the part of the ice shelf that remains connected to the continent.”
The BAS director added: “Our network of GPS instruments will give us early warning if the calving of this iceberg causes changes in the ice around our station.”