Channel 4 is to be privatised by the Tory government in a move set to spark furious backlash.
Ministers are expected to pursue a sale of the channel to private owners, a government source confirmed.
It would be the channel's biggest shake-up since it was founded in 1982.
Sir David Attenborough is among those who oppose the sale, according to the Mirror.
He supported a letter that urged ministers to 'stop short-sighted political and financial attacks' on public service broadcasters.
It came just hours before the channel became subject to a Government review.
That review warned "this is 2021, not 1982 - and the broadcasting landscape has changed beyond recognition. Increased global competition and changing audience habits pose challenges to linear TV broadcasters, including Channel 4 ".
The news was confirmed to staff in an e-mail by chief executive Alex Mahon.
He said the channel's "vision" for the next 40 years had been "rooted in continued public ownership", but "ultimately the ownership of C4 is for Government to propose and Parliament to decide."
Channel 4 is publicly owned and non-profit but receives no taxpayer cash, instead being funded entirely through its commercial activity.
Yet Culture Secretary Nadine Dorries, who is set to push through the sale, tweeted: "Channel 4 rightly holds a cherished place in British life and I want that to remain the case.
"I have come to the conclusion that government ownership is holding Channel 4 back from competing against streaming giants like Netflix and Amazon.
"A change of ownership will give Channel 4 the tools and freedom to flourish and thrive as a public service broadcaster long into the future.
"I will set out the future plan for Channel 4 in a White Paper in due course.
"I will seek to reinvest the proceeds of the sale into levelling up the creative sector, putting money into independent production and creative skills in priority parts of the country - delivering a creative dividend for all."
When the privatisation was floated last year, Labour insiders accused the Tory government of a "culture war" against the channel after one of its senior figures branded Boris Johnson a "known liar".
A spokesperson for Channel 4 said it was "disappointed" with the decision but would "continue to engage" with the Government on the process to "ensure that Channel 4 continues to play its unique part in Britain's creative ecology and national life".
The statement said: "With over 60,000 submissions to the Government's public consultation, it is disappointing that today's announcement has been made without formally recognising the significant public interest concerns which have been raised.
"Channel 4 has engaged in good faith with the Government throughout the consultation process, demonstrating how it can continue to commission much-loved programmes from the independent sector across the UK that represent and celebrate every aspect of British life as well as increase its contribution to society, while maintaining ownership by the public.
"Recently, Channel 4 presented DCMS with a real alternative to privatisation that would safeguard its future financial stability, allowing it to do significantly more for the British public, the creative industries and the economy, particularly outside London.
"This is particularly important given that the organisation is only two years into a significant commitment to drive up its impact in the UK's Nations and Regions.
"Channel 4 remains legally committed to its unique public-service remit.
"The focus for the organisation will be on how we can ensure we deliver the remit to both our viewers and the British creative economy across the whole of the UK.
"The proposal to privatise Channel 4 will require a lengthy legislative process and political debate. We will of course continue to engage with DCMS, Government and Parliament, and do everything we can to ensure that Channel 4 continues to play its unique part in Britain's creative ecology and national life."
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