The next boss of the BBC must be a Tory, according to the mayor of London, Boris Johnson.

Writing in the Daily Telegraph, he said the guarantee of funding from the licence fee left BBC staff with "an innocent belief that everything in life should be 'free'".

He said: "No wonder – and I speak as one who has just fought a campaign in which I sometimes felt that my chief opponent was the local BBC news – the prevailing view of Beeb newsrooms is, with honourable exceptions, statist, corporatist, defeatist, anti-business, Europhile and, above all, overwhelmingly biased to the left."

Johnson said the corporation treated eurosceptic views as "if they were vaguely mad and unpleasant" and "completely ignored" the private sector.

He said the next director general, replacing Mark Thompson, who is stepping down later this year, should be someone who is "free-market, pro-business and understands the depths of the problems this country faces. We need someone who knows about the work ethic, and cutting costs. We need a Tory, and no mucking around."

Conservative commentators have long taken aim at the BBC as a hotbed of leftwingers and Thompson has said it had been guilty of a "massive bias to the left" in the past.

He told the New Statesman two years ago that staff were "quite mystified" by the rise of Margaret Thatcher but now there was "less overt tribalism" among its journalists.

The current favourite to replace him as director general is the BBC's chief operating officer, Caroline Thomson, who worked as political assistant to Roy Jenkins in the SDP.

A BBC spokeswoman said: "BBC News is committed to impartiality and we reject Boris Johnson's assertions of bias.

"Our approach means asking difficult questions of politicians, businesses and unions alike.

"People with trenchant views often find this process uncomfortable but our audience expects us to challenge those in power, as well as those who seek it."

Johnson had a well-publicised run-in with a BBC reporter during the mayoral election campaign. He was caught on camera accusing Tim Donovan, BBC London's political editor, of talking "fucking bollocks" after he questioned Johnson's attempts to secure commercial deals with News International while the company was being investigated over phone-hacking.