Journalists from major news organisations across the UK boycotted Downing Street after some were ordered to leave.
Number 10 staff asked those not on a pre-selected list of journalists invited to a briefing on PM Boris Johnson's Brexit plans to leave.
This then prompted a walkout from colleagues across the media, including political editors Laura Kuenssberg from the BBC, Robert Peston from ITV and Beth Rigby from Sky News.
According to those present, when political correspondents arrived inside Number 10 they were asked their names and told to stand on opposite sides of the entrance hall - either side of a rug.
When questioned upon orders to leave The Independent's political editor Andy Woodcock said Number 10's director of communications Lee Cain told them: "We are welcome to brief whoever we want whenever we want."
The briefing was with David Frost, Boris Johnson's Europe advisor, on the PM's post-Brexit trade plans.
Certain journalists and media organisation were invite to Downing Street while others not on the list also tried to get it.
A Number 10 source said the Prime Minister's Europe adviser David Frost was due to speak to "senior, specialist members of the lobby" - a so-called "inner lobby".
The source added: "We reserve the right to brief journalists which we choose whenever we wish to, and that is not something abnormal."
They also said that "no one is banned - people are invited for an additional briefing, so that sort of language in itself is wrong."
The Daily Mirror's political editor Pippa Crerar said: "I felt deeply uncomfortable being left to stand on one side of the room while colleagues' names were read out one-by-one and they joined the group who were deemed 'acceptable' by No 10. Sinister and sad."
