TV newscaster Jon Snow has warned the Government not to privatise Channel 4, after Prime Minister David Cameron said he wanted to "look at all of the options" for the broadcaster's future.
Snow said privatisation would take up to £150 million a year out of programming and warned that the nightly hour-long Channel 4 News could be one of the first casualties.
Mr Cameron made clear at Prime Minister's Questions in the House of Commons that privatisation of the broadcaster was being considered.
He told MPs: "I want to make sure that Channel 4 has a strong and secure future and I think it's right to look at all of the options, including to see whether private investment into Channel 4 could help safeguard it for the future.
"Let's have a look at all the options. Let's not close our minds like some on the Opposition front bench who think that private is bad and public is good. Let's have a proper look at how we can make sure this great channel goes on being great for many years to come."
Labour said a Channel 4 sell-off was "clearly not in the public interest".
And Snow told BBC Radio 4's PM programme: "Channel 4 doesn't need private investment...
"We have here a channel that is generating £900 million-plus every year in profit, all of which goes back into programming.
"It costs the taxpayer not one penny and we in turn pay taxes into the Treasury."
He added: "Privatisation would require the owners to take a profit and that would mean £100-150 million of that £900 million would have to be taken in order to satisfy their needs."
He said this would hit the 350 small creative firms which provide Channel 4 programming - much of which he said would have no other terrestrial outlet.
And he warned: "Channel 4 News is a very expensive entity and we might well be one of the first casualties."
Snow said: "As it stands, (Channel 4) is a profitable and successful entity. Why tinker with it?"
Culture Secretary John Whittingdale said in August that a sale of Channel 4 was not currently being discussed.
But speculation over a sell-off was revived the following month when an official from his Department for Culture, Media and Sport was photographed entering Downing Street clutching a document which listed privatisation as one of the options for its future.
At PMQs, Scottish National Party MP John Nicolson called on Mr Cameron to confirm that "no discussions are under way to privatise and thus imperil this much-loved and important public institution".
Mr Cameron responded that he was "a huge fan" of the channel set up by Margaret Thatcher and wanted to explore all options to "safeguard it for the future".
Shadow culture secretary Michael Dugher said: "The Government has been misleading the public on their plans to privatise Channel 4 for months. First they said that ownership of Channel 4 was not 'under debate' and now the Prime Minister has finally come clean that they are drawing up options for privatisation.
"Channel 4 produces distinct and important public content and the broadcaster should remain not-for-profit. An ideological sale of Channel 4 is clearly not in the public interest. Labour will continue to stand up for Channel 4 and oppose any reckless attempts to privatise it."