The chairman of Channel 4 has warned Boris Johnson’s government not to go down the “high-risk and damaging path” of privatising the broadcaster.

       In a letter to culture secretary Oliver Dowden, Charles Gurassa said the government risks “sleepwalking into the irreversible and risky sale of an important, successful and much-loved British institution”.

       The government is consulting on plans to privatise Channel 4 – saying last month that moving the broadcaster into private ownership could ensure its “future success”.

       Mr Gurassa wrote to Mr Dowden: “We look forward to engaging in a constructive dialogue with you … However, we are deeply concerned with the unsubstantiated assertion that a sale of Channel 4 is in the national interest.”

       He added: “Without a transparent assessment of the implications of such a decision, the government is in danger of sleepwalking into the irreversible and risky sale of an important, successful and much-loved British institution.”

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       The channel, which was founded in 1982 to deliver to under-served audiences, is owned by the government and also receives funding from advertising.

       The Department for Digital, Culture, Media and Sport (DCMS) said the decision to review Channel 4’s ownership structure had been taken because the changing media landscape posed a serious threat to traditional broadcasters.

       In his letter, Mr Gurassa trumpeted the channel’s financial health and said it has a “clear plan” moving forward.

       The board said it shares the government’s ambition for the channel since the organisation “thrives on change ... sticking with the status quo is not the modus operandi of Channel 4, and never has been”.

       The letter touted the board members’ experience in the private sector – but questioned if that was the best environment for Channel 4. “It is thriving without any taxpayer support and in addition is delivering a unique range of public obligations and broader economic benefits,” it said.

       The letter also states: “We have serious concerns that the consequences will be very harmful, both to the UK’s creative economy and to the choice and breadth of distinctive British-made content available to UK audiences.”

       And Mr Gurassa wrote: “Channel 4 is not an inefficient state-owned monopoly, but an agile, innovative challenger with a public purpose at its heart. It is efficient, well run, and on a sure footing to tackle the future challenges facing the sector.”

       A government source said: “The Channel 4 model is facing increasing pressure from competition for viewers from high-spending streaming giants and growing pressure on the advertising revenue on which it solely depends.

       “We’re looking at reform to protect Channel 4’s long-term future so it can continue serving audiences with great public service content for decades to come.”