BBC News is braced for cuts of £80m over the next four years as the corporation as a whole looks to save £550m a year by 2021-22.

James Harding, the BBC’s head of news, warned staff on Monday that his “working assumption” of how much the division would be hit by the BBC’s cost-cutting proposals was about £80m.

BBC News, which employs about 7,400 of the corporation’s 18,000 workforce, has already announced £5m in savings as part of the corporation’s overall target of £150m in annual savings by 2017.

Although he declined to reveal which departments or services would bear the brunt of the cuts, speculation continues to focus on the future of Radio 5 Live, the News channel and local news. All three could prove politically sensitive, however.

The BBC news channel costs £63m a year but much of the costly news gathering provided for the channel is used elsewhere in the BBC. Newsgathering in total is the biggest single cost in the whole department.

Radio 5 Live employs fewer people but has a similar annual budget – £66m – because of the high cost of sports rights. The BBC is looking to make the station online-only because so many consume sports news in this way, but Radio 5 Live is broadcast from MediaCityUK in Salford and is a department of BBC North, which would make such a cut politically sensitive.

Another potential victim of the need to find savings to cover the £700m annual cost of free TV licences for the over-75s by 2020 is thought to be local radio, which costs £153m a year. However, the BBC last year said it wanted to expand its local provision with another 100 reporters, a plan that was met with some opposition from commercial rivals.

The announcement follows a three-month Future of News project, which was launched in January. Final proposals are set be announced at the end of March.

Harding told staff last year that the BBC would not make any long-term decisions on the channel while doing more work developing video news for smartphones.

A BBC spokesperson said after the internal presentation to staff in London: “No decisions have been taken and no recommendations have yet been made about the future of BBC News.”

When he launched the three-month review to reshape the department for the next decade, Harding said BBC News “can’t afford to do everything” and that 2016 would be a “defining year” for the division.

“We are going to have to make choices,” he wrote in a blogpost to staff. “Technology is transforming the news. Audience expectations are changing, too. And the funding settlement for the BBC requires both cuts and the reallocation of spending.”

As part of the review, the BBC is understood to have set up four working groups to look at output (programmes and platforms such as the news channel and local radio etc), content, audiences – and one on working practices.