BBC director-general Tony Hall (pictured, Reuters) has warned staff the corporation's independence will be challenged and it will face "naked bullying" in the run-up to the general election and next year's charter review.

It was a moment of "high risk" for the corporation, he told staff in central London.

"And there may be some – I hope only a few – who try to use the impending charter review to influence our coverage of politics in this most sensitive of political years. We will never let that happen, because to do so would betray the public and the ideals of the BBC," he said.