Mark Thompson, the BBC's director general, said British broadcasters should be free to launch an equivalent to Fox News in the UK because existing rules to guarantee impartiality in television were becoming outdated in the era of the internet.

Thompson, while speaking at a Whitehall seminar on impartiality in broadcasting, said that as the distinction between the web and television collapses, it no longer makes sense for public service broadcasters such as the BBC, ITV and Channel 4, to have a "monopoly" over the airwaves.

The director general said: "There was a logic in allowing impartial broadcasters to have a monopoly of the broadcasting space. But in the future, maybe there should be a broad range of choices? Why shouldn't the public be able to see and hear, as well as read, a range of opinionated journalism and then make up their own mind what they think about it?

"The BBC and Channel 4 have a history of clearly labelled polemical programmes. But why not entire polemical channels which have got stronger opinions? I find the argument persuasive."

So unexpected was Thompson's intervention that his remarks caught some of the BBC's best known journalists unawares. Nick Robinson, the BBC's political editor, who chaired the debate on Thursday evening, admitted the DG's plea for regulatory liberalisation had "slightly taken me by surprise".

Thompson said that the BBC News services would remain impartial, but he added that views regarded as "extreme" could and should be broadcast by the BBC even within the current rules on impartiality.

The BBC had been, historically, "weak and nervous" about airing debates about immigration and Europe, he said – but added that he believed the public broadcaster had forced the main parties to discuss immigration during the 2010 election campaign. He promised that there would be more space for "extreme and radical perspectives" on the BBC, which one day could become common views.

In the US, strong opinion had won the ratings battle, with the right-wing Fox News getting a larger audience than CNN, Thompson said. But that needn't be replicated in Britain. "I don't believe that necessarily means you get the dire consequences that some people see in America. Having a broader range of channels would actually strengthen that enduring tradition of impartial journalism across BBC, ITN and Channel 4. They would continue to be trusted.

"Impartiality is sovereign for the BBC. The premium on impartiality would grow. But I'm not convinced that the public service broadcasters need to have a monopoly over news for ever." During the debate it was suggested the Daily Mail newspaper should be free to set up its own opinionated news station if it so wished.

Ironically, Thompson's proposal makes him an ally of the Murdoch family. The BBC director general told the audience that Rupert Murdoch had told him he would like Sky News to go down a polemical "Fox-style" route – but that the editors of the channel had brushed off his wishes.

Kelvin MacKenzie, the former editor of the Sun, also on the seminar panel, said he should be able to host a debate about immigration or Britain pulling out of Europe without having to present a countervailing point of view.

MacKenzie said he had recently discussed with David Cameron his own idea for a radio "free for all", with talk stations allowed to say what they want, free from Ofcom regulation. The prime minister apparently replied "erm…" and then said it was an interesting idea for radio but the experiment probably wasn't suitable for television.