The BBC’s head of news Helen Boaden and her deputy Stephen Mitchell have been replaced pending the outcome of an internal review into how the corporation handled sexual abuse claims against former presenter Jimmy Savile.

The news came two days after director general George Entwistle resigned after just 54 days in the job, making him the corporation’s shortest-serving head.

What is happening at the BBC?

Mr Entwistle resigned as the BBC’s director general on Saturday, less than two months after taking charge. He quit “in the light of the unacceptable journalistic standards” of a report Newsnight – one of the BBC’s flagship current affairs news programmes – broadcast about sex abuse at a children’s home in Wales in the 1980s.

In the report, a former senior Conservative politician was wrongly accused of child abuse. Ten days later it was announced that the BBC’s head of news, Helen Boaden, and her deputy, Stephen Mitchell, had been asked to step aside pending a report on why an investigation into separate abuse claims against a former presenter, Jimmy Savile, never ran.

How did this start?

In December 2011 Newsnight decided not to air an investigation into claims that Savile, a star BBC presenter from the 1960s to 1980s who had recently died, had sexually abused young people.

In October rival broadcaster ITV aired its own programme on the allegations, which added to a flurry of further accusations against Savile. This in turn led to mounting questions about why the Newsnight programme was dropped, and whether there was a cover up.

A number of investigations were launched inside and outside the BBC. The editor of Newsnight, Peter Rippon, stepped aside on 22 October pending the result of an investigation by a former head of Sky News, Nick Pollard.

On 2 November Newsnight aired a separate programme on alleged abuse at the children’s home in Wales, in which a witness claimed that a Conservative politician abused him a number of times.

Though the programme did not name him, speculation on the internet either names or implicated former treasury minister Lord McAlpine. A week later, Lord McAlpine issued a denial, and Newsnight’s witness apologised for the case of mistaken identity. The BBC then issued an unreserved apology. You can see a timeline here.

How is it affecting output? Should audiences worry?

There was an “immediate pause” in all Newsnight investigations ordered when the problems with the 2 November programme became apparent. But other broadcasts on the BBC have carried on as before.

Acting director general Tim Davie, told staff by email on Monday that there would be “no handbrake turn” on Mr Entwistle’s plans for “getting rid of anything that gets in the way of delivering the best of British creativity to our audiences”.

What is the BBC editorial chain?

At the time of the Newsnight investigation into Jimmy Savile, editors on the programme answered to Mr Mitchell, deputy director of news and head of programmes. His boss was Ms Boaden, the head of news, who in turn answered to the director general.

When the investigation into the Savile programme was announced, Ms Boaden and Mr Mitchell were recused from overseeing coverage related to Savile story. See a chart of the editorial chain of command here.

Why is this important?

The BBC is a public service organisation, financed within the UK by a licence fee paid by British residents. Throughout its history it has built up a reputation for trust and reliability both within the UK and beyond. It has fiercely defended itself against outside interference, especially from the UK government. Its dominance, both because of its size and because of the reach of its output, has frequently come under criticism from commercial rivals.

What is the government’s position?

Prime Minister David Cameron has referred to the problems facing the BBC as “very difficult, very serious”, but has said he does not believe that the corporation is facing “an existential crisis”. Mr Cameron’s office did however question a 12-month, £450,000 ($714,000) payoff for Mr Entwistle, which it described as “hard to justify”.

Is this the first such crisis at the BBC?

Mr Davie described the last few days and weeks at the BBC as “exceptionally tough”, but the BBC has been through serious crises before.

In January 2004 Gavyn Davies, the chairman of the BBC’s board of governors, and Greg Dyke, the director general, both resigned in the wake of an inquiry that criticised the BBC’s handling of a report about intelligence in the run-up to war in Iraq.

In 1987, another director general, Alasdair Milne, was forced out after a series of disagreements with the Conservative government of Margaret Thatcher.

The BBC has clashed several times with governments over coverage of conflicts involving British troops. In 1956, the conservative government was upset by coverage on the BBC of divided opinion about the decision to recapture the Suez Canal from Egypt. Schemes to “discipline” the corporation were discussed, which are believed to have included the government taking editorial control of the BBC. Ultimately, there were no sanctions and the BBC’s reputation for impartiality survived more or less intact.

Also see “Entwistle urged to consider giving up half of his £450,000 severance payment at: http://www.bbc.co.uk/news/uk-politics-20295434

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