The country's other major co-ops - First Milk, Milk Link and Dairy Farmers of Britain - confirmed they were in active discussions with the receivers.
PricewaterhouseCoopers was brought in by United Milk's directors following a long period of losses since the co-operative started trading from its £45m butter and milk powder processing plant last year.
PWC is keen to keep the plant running. It can process 800 million litres, making it the largest in the UK.
The National Farmers' Union said it was shocked at the news. "It will be a particular concern to UK dairy farmers who regarded United Milk as a major asset to the dairy industry."
Jim Begg, director of DIAL, the dairy industry's trade assocation, said: "We are said to see this happen to another manufacturing plant. But it shows how tough the market is."
The news comes almost exactly a year after another major diary farmer co-operative, Amelca in Derbyshire, also went into receivership.