The term ‘speaking truth to power' stems from the American civil rights movement in the 1960s. It was coined by Bayard Rustin and referred to the highly visible and public stand taken by black activists to speak the truth about the extreme racial injustice they experienced in their everyday life. Since then, the term has been used in very many different circumstances: from standing up to powerful forces, to speaking truthfully to powerful individuals.
It has also been misused by Whitehall commentators about how senior civil servants should proffer advice in private to their political masters. And following this, the term has been further misappropriated to apply to how senior local managers should advise locally elected politicians.