Political reporters staged a walk-out in Downing Street today in protest at attempts By Number 10 to prevent several news organisations from a Government Brexit briefing.

Senior figures from the Daily Mail, Times, Sun, BBC and Sky were among those who refused to attend the event with David Frost, Boris Johnson's Europe advisor, in Westminster today.

They had been invited to the technical non-political briefing by the civil servant, but organisations including the Mirror, Independent, PA Media and the Huffington Post had not.

When senior political staff from those organisations learned of the briefing they came to Downing Street.

But once inside they were separated from those with invitations and told to leave.

When senior political staff from those organisations learned of the briefing they came to Downing Street. But once inside they were separated from those with invitations and told to leave.

All the approved journalists then took the decision to walk out with them in solidarity, including the BBC's Laura Kuenssberg and ITV's Robert Peston.

Mirror Political Editor Pippa Crerar, who was among those refused entry, tweeted: '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.'

A No 10 source said the briefing had been meant for a select group of reporters called the 'inner lobby' that has been operating since last summer, when Boris Johnson became Prime Minister.