Thousands of BBC journalists are on strike in a row over pensions which will disrupt radio and television schedules on Friday.
Presenters including Fiona Bruce and Huw Edwards are reported to be joining the action, which is expected to hit news bulletins and see flagship shows Newsnight and Radio 4's Today programme taken off air.
Members of the National Union of Journalists (NUJ) began their 48-hour walkout at midnight on Thursday. They plan to strike again on November 15 and 16, with threats of further disruption over Christmas.
The move follows a 70 per cent rejection of the BBC's "final" offer on pensions, which the union described as making journalists "pay more, work longer and receive lower pensions".
The BBC would not discuss how the walkout could affect programmes but said the organisation had "contingency plans" to cope with its effects.
Picket lines were being mounted at sites across the UK, including Bush House, Broadcasting House and the TV Centre in London.
The NUJ said it expected "widespread support" from journalists for the strike and predicted that members of other unions which have accepted a deal on pensions could also refuse to cross picket lines.
Martha Kearney and Kirsty Wark are among other high-profile names said to be taking part. The BBC 1 Breakfast show and Radio 5 Live Breakfast show are expected to be affected, with Radio 4 programmes The World at One and PM also hit.