James Harding is to stand down as director of news and current affairs at the BBC and set up a media company that will offer “a clear point of view”, a perspective the impartial corporation is not allowed to provide.

The £340,000-a-year executive had been considered one of the frontrunners to eventually succeed Tony Hall as director general of the BBC, but his sudden departure leaves the director of radio, James Purnell, as the favourite.

Explaining his decision in a letter to staff, Harding wrote: “There is some journalism that the BBC, for all its brilliance, can’t, and probably shouldn’t, do. And that’s what I want to explore: I am going to start a new media company with a distinct approach to the news and a clear point of view.

“I know I will enjoy the chance to do some more journalism of my own and, at such a critical time, I’m seriously excited about the prospect of building a new venture in news.”

It is understood that Harding, who will leave the BBC early next year, has backers for his project and that it will focus on analysis rather than news. The 48-year-old joined the BBC in 2013, having left his previous role as editor of the Rupert Murdoch-owned Times newspaper the year before.

BBC sources insisted Harding’s departure was not connected to any internal clash about the director general role and that Hall intended to be in charge for years to come.

Another source said they suspected Harding wanted to “rediscover his voice” after being at the brunt of criticism from across the political spectrum about the BBC’s news coverage during his four-and-a-half years in the role.

Critics of the BBC have claimed its coverage of the Scottish independence referendum, Brexit and Jeremy Corbyn was biased.

Boris Johnson, the foreign secretary, accused the BBC of “shamelessly anti-Brexit coverage”, while the BBC Trust ruled in January that a report about Corbyn’s views on shoot-to-kill policies breached impartiality and accuracy guidelines, a decision Harding opposed.

Julian Knight, a Conservative MP and member of the influential digital, culture, media and sport select committee, said: “Harding always felt an odd match for BBC News and his departure statement, where he says he wants to pursue stories which BBC News wouldn’t do, reflects that.

“The important thing is that in the post-Ofcom regulation world the BBC doubles down on impartiality and sets out to retain its position as a gold standard for news and current affairs.” 

This year, Harding has had to deal with a series of pay rows at BBC News, including the pay gap between male and female presenters and between BBC World Service and other news staff.

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The BBC is reviewing the pay of its leading broadcast journalists as well as the terms and conditions of all staff. Harding has been heavily involved in the reviews and has also been trying to cut £80m from the news budget.

Despite these pressures, Harding said in his letter to staff that the BBC had renewed its reputation for strong, responsible reporting.

“We have our shortcomings, no doubt. But, in these fast-changing times and on the back of a crisis five years ago, I am proud to have worked for BBC News as we renewed our reputation for responsible, powerful journalism: agenda-setting coverage of politics, business and the society we live in; current affairs exposing controversial issues with discipline and determination; the best and bravest international reporting, when big moments in history unfold and when under-reported stories desperately need to be told.”

Hall said Harding had left a “great legacy” as head of news.

“James has done an incredible job during a hugely complex and momentous period of British and world history,” he said, including two referendums, two general elections and the US presidential election.

“He supervised lasting changes to programmes and services while also appointing a range of new editors, on-air and off, including the appointment of the BBC’s first female political editor. James has launched slow news and Reality Check to counter fake news.”

Other “significant achievements” included the rollout of a dozen new World Service language services, and the development of digital storytelling, such as news for mobile devices, Hall said. 

The BBC will consider internal and external candidates to replace Harding, who worked at the Financial Times for 12 years before joining the Times in 2006 as business and City editor. Hall said he would appoint Harding’s successor by the end of the year. The favourites for the role include Francesca Unsworth, Harding’s deputy and the head of the World Service.