Lisa Nandy, the culture secretary, has warned that Russell Brand’s conviction for rape and sexual assault must be a “wake-up call” to the media world and beyond, after widespread concerns over the failures to confront his behaviour.

With renewed calls from TV insiders for a new examination of how Brand’s treatment of women was tolerated for so long, Nandy said the case was a “defining moment for our country”.

Nandy called on employers to ensure vulnerable whistleblowers are protected. It follows concerns raised during Brand’s trial that some women thought they would not be believed because of his status.

“Yesterday’s ruling must mark a defining moment for our country,” Nandy said. “It is only because of the bravery of the women who came forward that action was taken. If it wasn’t for them and the persistence of a handful of journalists, justice would not have been done. They remind us why a free press matters.

“This must now be a wake-up call.…