The BBC Director General Tony Hall has said he will not reveal how the BBC learned about a police warrant to search Sir Cliff Richard's home in advance.
In his letter to Home Affairs Select Committee chairman Keith Vaz, he said the anonymity of sources was "a key principle for all journalism" and "for that reason the BBC will not be providing details about the source".
He added that the BBC was an independent organisation and that he would not "elaborate on detail of our editorial processes".
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