Andy hughes,
Allegations were made about famous people, and then a photograph was shown to established that the named person(s) were the same.
The BBC probably adopted this procedure after the Newsnight Lord McApline debacle. Someone called Steven Messham named McAlpine as someone who had abused him, and it was only when the allegation had been broadcast that Messham saw the photo of McAlpine, and it wasn't the person who had abused him.
// Messham, the star witness, delivered the coup de grace: he called Stickler to say, now having seen a photograph of Lord McAlpine, he had not been his abuser. //
McAlpine sued and the BBC had to pay damages. A simple check by photo would have prevented the false naming of McAlpine. So showing a photo to a different witness who had named Leon Brittan is meant to be a precaution to prevent mistaken identity.