BBC Radio 4's flagship Today programme was disrupted this morning as thousands of journalists staged a second one-day strike in protest at compulsory redundancies.
The first one-day strike also led to severe disruption of news output and took place on 15 July.
The programme went on air at 7am, an hour later than usual, as members of the National Union of Journalists (NUJ) took industrial action across the UK.
Picket lines were mounted outside studios and offices, including the BBC TV Centre in west London, Bush House in central London and cities including Belfast, Glasgow and Manchester.
The union said early reports were that the strike was being "solidly supported" by the 3,000 NUJ members at the corporation.
BBC Radio 5 Live was hit this morning, playing pre-recorded programmes to replace its regular Up All Night show.
NUJ general secretary Michelle Stanistreet joined a picket line at TV Centre shortly after midnight and will address strikers outside Bush House later today.
She said journalists were angered at a "change in approach" by the BBC to job cuts, with a number of compulsory redundancies already made and more expected in the coming weeks.
The two sides will meet for talks on 11 August, but the NUJ leader said: "There has been absolutely no meaningful movement from the BBC to address the cases of individual journalists losing their jobs now."
A BBC spokesman said: "We are disappointed that the NUJ is intending to strike and apologise to our audience for any disruption to services this may cause.
"Industrial action will not alter the fact that the BBC is faced with a number of potential compulsory redundancies, following significant cuts to the central government grants that support the World Service and BBC Monitoring.
"We will continue with our efforts to reduce the need for compulsory redundancies; however, the number of posts that we are having to close means that, unfortunately, it is likely to be impossible for us to avoid some compulsory redundancies."
An NUJ spokesman said: "All the journalists currently affected are willing to accept redeployment and they face an uncertain future through no fault of their own.
"The BBC is wasting thousands of pounds making skilled and experienced people compulsorily redundant instead of redeploying staff. This is money that should be used to make better programmes and to ensure the future of quality journalism at the corporation."
NUJ members working for the BBC's Arabic service were on the third day of a six-day strike in a separate dispute over rotas.