On Monday night, millions of iPhones in Britain buzzed with a push notification encouraging their users to watch three video clips that were said to “sum up a difficult start to election week for the Tories”.

Anyone who clicked through would have been offered an “awkward exchange” as the prime minister grabbed an ITV reporter’s phone, Labour activists heckling the health secretary, Matt Hancock, at a hospital in Leeds, and Boris Johnson trying to rebut claims that Priti Patel had made up crime figures.

What many might not have known is why they received the push alert. They may have been surprised to learn that the clips were chosen not by an algorithm but by Apple News’s five-strong team of UK editors.

The service has around 11 million users a month in the UK, according to Comscore data, and the number of people receiving its notifications is even larger, offering a level of direct access that even the BBC struggles to compete with.

While newspapers and TV channels have to fight to reach audiences, Apple News comes pre-installed on iPhones. And while traditional news outlets come under enormous scrutiny for their coverage, there has been little scrutiny of how journalists employed directly by Apple can influence which news is seen by around a sixth of the UK population.

Rasmus Nielsen, of the University of Oxford’s Reuters Institute for Journalism, believes the power of the service – and equivalents such as Samsung’s Upday - is under-appreciated. “Our data suggests that more than a quarter of online news users in the UK rely on one or more aggregators for online news, and Apple News and Google News have higher reach among people aged 18-24 than established brands like ITV and Sky or the Sun and the Mirror,” Nielsen said. “Their editorial processes, however, remains opaque, whether reliant on human editors, algorithms, or some combination.”

Journalists who work for Apple News have scrubbed the company’s name from their social media accounts, a move that reduces the risk of them being accused of bias but adds to the lack of transparency around their decisions.

People at British media organisations who deal with Apple News say the editors have a welcome reputation for promoting exclusives and high-quality news featuring original reporting in their “top stories” section. If the Apple News editors like what they see, their backing can deliver enormous numbers of readers – which gives these editors a power akin to an old-school newspaper boss choosing a front-page story.

“You could get a million views in the UK alone if they pick one of your stories,” said one social media manager at a British news site, who suggested outlets were hooked on traffic from the service. Although news websites struggle to make money from Apple News traffic, they are often loth to give up a source of traffic that can refer more readers than Facebook.

Apple News staff will tell British news outlets what type of stories and topics they would like to promote each week, creating the potential that one of the world’s biggest hardware manufacturers is indirectly influencing the editorial output of British news organisations.

Much of this reflects a decision to stick to promoting mainstream outlets as part of Apple’s attempt to ensure a high quality of news stories, as opposed to the chaotic free-for-all news environment of Facebook or Twitter. This can be a boon for traditional news organisations such as the Sun and Daily Telegraph, which are well represented alongside left-of-centre outlets such as the Mirror, HuffPost and the Independent.

(The Guardian is not on Apple News. A spokesperson for Guardian News & Media said the company was in preliminary discussions about returning to the service in the future if it “would help to deliver our strategy to develop new and engaged audiences for Guardian journalism”. No firm decision has been made.)

Apple declined to comment on the record on how Apple News worked but provided a comment from its editor-in-chief, Lauren Kern, setting out its plans for covering the general election.

“Curation has always been a guiding principle of Apple News. We select high-quality articles from trusted sources to help readers get up to speed on the most relevant news and the most important issues of the day,” Kern said.

“In the UK election guide, our team of editors will spotlight well-sourced, well-reported stories to provide Apple News readers with reliable news and information from a wide range of news outlets.”