Lord Bragg has hit back at Lord Birt over the former BBC director general's recent criticism of ITV.
Lord Bragg is also controller of arts and features for Granada Television
Lord Bragg said he was "saddened" after the peer said the channel was "clinging on to the public service tradition by its fingertips" in a speech last month.
He said: "Perhaps he has joined that club of beached grandees who take swipes at ITV, whose programmes they might not have even watched."
He added the peer had been "cavalier" and had "no right" to dismiss ITV.
His comments came after the former BBC director general gave his views in his James MacTaggart Memorial lecture at the Edinburgh TV festival last month.
Lord Birt was director general of the BBC from 1992 - 2000.
In a speech calling for "more truth and beauty" from programme makers, Lord Birt said: "The main consequence of the explosive growth in the number of channels is that ITV - whose share has particularly tumbled - is clinging on to the public-service tradition by its fingertips.
"When the analogue switch-off occurs, and when ITV is more or less on a level playing field with a welter of commercial competitors, it will no longer be, in any meaningful sense, a public service broadcaster."
But Lord Bragg said he was "disappointed" that Lord Birt - who he said he still admired as a broadcaster - had joined "the feeding frenzy" by ITV's critics.
At the launch of the new series of The South Bank Show, the ITV1 arts documentary series he edits and presents, he said: "ITV is still unique as a commercial broadcaster of great success and as a public service broadcaster of distinction.
"It is the only creditable competitor to the BBC. John had no right to dismiss it in that cavalier way."
Lord Bragg said that broadcasting Coronation Street, Emmerdale and Ant and Dec meant ITV held "some of the biggest cards in the British TV pack".
Lord Birt was unavailable for comment.
Lord Birt was BBC director general from 1992 to 2000
Meanwhile, The South Bank Show has been recommissioned until 2007, the longest contract in its 26-year history.
ITV director of programmes Nigel Pickard said: "I hope this investment dismisses the idea that ITV is abandoning its heritage."
The autumn series includes programmes on playwright Alan Bennett, comic Eric Sykes, violinist Maxim Vengerov and TV comedy Little Britain.
Lord Bragg is also to present a new four-part ITV1 series on the 12 books he thinks have changed the world.
Beginning next April, the series will include the King James Bible, William Shakespeare's first folio, Charles Darwin's Origin of Species and the first rulebook of the Football Association, published in 1863.