The veteran filmmaker suggested Robinson had ousted himself as a Conservative in a recent tweet which claimed the Labour leader was “long on passion and short on details”.
Appearing on stage at the Communication Workers Union event, Loach read out the tweet which was sent last Thursday.
“The Today Programme on BBC have a presenter called Nick Robinson,” the 80-year-old said prompting audible boos from the audience.
“He showed his impartiality yesterday. Did anybody read this? He said ‘No one should be surprised that Jeremy Corbyn is running against the Establishment and is long on passion and short on details. Story of his life’.”
“That’s Nick Robinson, ex-member of the Conservative Party," Loach continued. "That’s the partiality of the BBC. That’s the bias we have to complain about. That’s what we have to fight.”
Before embarking on a career in journalism, Robinson was President of the Oxford University Conservative Association.
Loach, who is famed for making films which explore social issues such as poverty and labour rights, argued Mr Corbyn had been on the “right side of history” throughout his life.
Responding to the speech, Robinson insisted he gave "impartial interviews".
"I judge Ken Loach by the quality of the work he produces," he told The Independent. "He is a great film maker. I think he should judge me in the same way - by the impartial interviews I do which are rigorous with all sides"
Robinson sought to clarify the controversial tweet in a Facebook post at the time.
“When I tweeted earlier that people should not be surprised by Jeremy Corbyn's approach as it was ‘the story of his life’ some read it as being pejorative and evidence of that establishment sneering. I meant no such thing,” he wrote.
“My point was that the Labour leader is doing what he has done for decades and what brought him huge and unexpected success in his party. So no-one should expect him now to change his approach.”
“I, on the other hand, will read my tweets twice to check they don't read as if I mean something I never intended.”
A representative for Loach did not immediately respond to request for comment.
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