British journalists walked out of a government briefing on Monday in protest at the exclusion of other reporters, in the latest tensions between Prime Minister Boris Johnson's team and the media.
It is not unusual for political advisers to speak to select journalists but there was concern that Monday's incident involved a supposedly neutral civil servant, diplomat David Frost.
A number of political reporters were invited to a briefing on Britain's post-Brexit trade strategy in Johnson's Number 10 Downing Street office.
When others whose names were not on the list arrived, they were told to leave, according to the accounts of several journalists who were there. All the reporters then walked out in protest.
Johnson's office declined to comment to AFP inquiries but the Independent newspaper reported a response from his director of communications, Lee Cain.
"We are welcome to brief whoever we want whenever we want," Cain told reporters at the event.
Michelle Stanistreet, general-secretary of the National Union of Journalists (NUJ), said it was a "very alarming incident."
She noted the government was already boycotting certain programs, notably by refusing to send ministers on BBC radio's flagship current affairs program "Today."
"Johnson's government must stop this paranoia and engage with all the press, not just their favorites," she said.
There have been rising tensions between Johnson's team and political reporters based in parliament, known collectively as the lobby.
Several media groups raised concerns last month when the government moved daily lobby briefings from parliament to a room in Number 9 Downing Street, which is behind a security gate.