Just before the evening news in Hong Kong on a Monday in July, Asia Television (ATV), one of the city’s two free-to-air TV stations, was showing a documentary produced by China Central Television (CCTV), the state broadcaster.

The screen showed grainy old images, shot during the 1950s, of workers clearing a road through Tibet’s mountainous landscape. The narrator explained that “Chinese and Tibetan soldiers and civilians worked shoulder to shoulder”, building highways that turned Lhasa “into a modern city overnight” and “made Tibetan butter tea an affordable luxury for the province’s grateful citizens”. It is a picture of fraternal harmony that accords ill with the riots and deaths in the country this March, but one well attuned to the antennae of the rulers of Hong Kong, back in Beijing.

Observers say ATV’s Beijing-friendly stance has become more overt in recent years, since businessmen with strong mainland Chinese interests took large stakes in the company. Its choice of programming is only one indication of this; another is still more obvious. Beneath its logo at the corner of the screen, the station now displays the slogan “China Stand Strong!”

Nearly 15 per cent of the unlisted ATV is held by a subsidiary of Citic Group, the Chinese state-controlled investment company. ATV this year started carrying one of CCTV’s stations on digital TV – the first time that a Chinese state channel has been broadcast in Hong Kong.

For activists and media watchdogs, this raises troubling questions about freedom and impartiality. These are sharpened further by the fact that a big stake in Television Broadcasting (TVB), ATV’s much larger rival, is set to be sold to a mainland property tycoon. Sir Run Run Shaw, TVB’s centenarian chairman and biggest shareholder, is expected to sell his 26 per cent stake to Yeung Kwok-keung, whose Country Garden is China’s biggest property developer by market capitalisation.

Hong Kong has enjoyed a relatively free flow of information since the former British colony returned to Chinese rule in 1997, and boasts a large number of newspapers and magazines. But television is, as everywhere, by far the more popular medium. The city’s 7m people still largely rely on the free services provided by ATV and TVB, and concern is growing that these channels are looking more frequently over their shoulder to Beijing.

Serenade Woo, Hong Kong project co-ordinator for the International Federation of Journalists, said there is concern over how Mr Yeung, a “red businessman”, would run TVB. “Would he get rid of certain programming just because they don’t attract high ratings? What would his bottom line be [when it comes to politically sensitive reporting]?” she asks.

While the Chinese government has no official means of interfering with the share sale process, analysts and academics say the importance of TVB as Hong Kong’s biggest TV station means that it is almost unthinkable that the company would be sold to foreign buyers or those who are considered hostile to Beijing. Hence the questions over Mr Yeung’s ownership – which are the more urgent because he was practically unknown in Hong Kong until Country Garden listed on the city’s stock exchange in 2006.

Even with that listing, his profile remains low – although his daughter, Yang Hui-yan, last year became China’s richest person. Ms Yang is worth US$17.5bn, according to Forbes, thanks to Mr Yeung’s transferring his entire stake in Country Garden to her before the listing.

TVB’s employees, who spoke on condition of anonymity, tell of a history of shifting towards Beijing’s news values, predating Mr Yeung’s control. “Efforts to limit editorial freedom already exist,” said one TVB reporter. “The change [over the past few years] at TVB is not as obvious as at ATV but some of the reporting is slanted already. It has been especially the case since the station started trying [to] break into the mainland China market several years ago.”

A comparison of the two stations’ coverage of politically sensitive events, such as the annual June 4 vigil commemorating the 1989 Tiananmen massacre, highlights such changes, the reporter said. “For June 4, we can no longer show anything calling for the end of one-party rule in China, but at least we can still show slogans such as ‘Rectify the June 4 Verdict’, which ATV no longer does.”

TVB said its news programmes always enjoyed editorial independence and declined to answer further questions, saying they were hypothetical.

Brian Wong, a veteran journalist who has worked in media organisations including ATV and TVB for more than two decades, said self-censorship by frontline reporters was the key limit to editorial freedom in Hong Kong. He pointed to an example of an ATV reporter, covering a mass protest of 500,000 people against Tung Chee-wah, Hong Kong’s former chief executive, who had muted the shouted slogans for Mr Tung to step down.

“The reporter thought that the original footage [with the sound turned up] would not be allowed to go on air. So instead of having to make changes at the last minute if the supervisors rejected it, the reporter thought it would be easier to just turn down the volume,” Mr Wong said.

Jackie Sam, acting chairman of the Hong Kong Journalists’ Association, said self-censorship was commonplace among Hong Kong’s media. “Most of the journalists know on which side their bread is buttered,” he said.

The dangers of such self-censorship to press freedom were emphasised by Martin Lee, one of the most prominent leaders of the city’s pro-democracy movement, who is to retire from the legislature this year. During one of his farewell speeches, he warned: “If you sacrifice press freedom when you are in a good position to enjoy it, don’t blame others [when you lose those freedoms] ... you alone are to blame.”  Additional reporting by Aiko Stevenson

This article is part of a series on television round the world. For earlier pieces, visit www.ft.com/arts/tv