BBC radio and TV programmes have been disrupted because of a strike by journalists and technical staff in a row over jobs, workload and claims of bullying, with threats of further stoppages to come.
The strike led to the cancellation of BBC Two's Newsnight, Radio 4's PM and World Tonight, pre-recorded interviews being used on the news channel as well as other changes.
Members of the National Union of Journalists (NUJ) and the technicians' union Bectu walked out of offices and studios across the UK at noon on Thursday and will follow the action with a work to rule.
Unions mounted picket lines outside BBC centres, including New Broadcasting House in central London, where strikers held up banners and wore badges which read Fight For The BBC.
The unions were protesting at the so-called Delivering Quality First (DQF) programme which will lead to 2,000 job losses.
The BBC apologised for disruption caused by the strike but said it could not agree to union calls for compulsory job losses to be postponed.
Michelle Stanistreet, general secretary of the NUJ, said workers were sending a clear message to the BBC that it needed to address problems created by the "ill-conceived and badly-implemented" cuts.
Gerry Morrissey, general secretary of Bectu, told the strikers that a meeting had been arranged with new BBC director general Tony Hall next month, when he will be urged to try to renegotiate the licence fee with the Government.
He said further strikes will be held unless the deadlock is broken.
A BBC spokesman said: "We are extremely disappointed that the unions have gone ahead with the strike and apologise to our audiences for the disruption to services."