Is there a finer “king” actor living than Ian McDiarmid? He is not cut from the traditional cloth, being slight of figure; but he has something in his bearing that, as Kent says of Lear, we would fain call master. And even more so in his voice: whether as Marlowe’s Edward II, Pirandello’s Henry IV or George Lucas’s Emperor of the known galaxy, those at once mellifluous yet abrasive tones convey knowledge, guile, control of whatever kind is required at that instant. (Indeed, I have to admit that at one or two moments in every performance I find myself thinking, “Ah, he’s using his Star Wars Emperor voice here...”) As Frederick William I, Elector of Brandenburg, he embodies Prussian rectitude, condemning his adopted son (the prince of the title) to death for winning the Battle of Fehrbellin but deviating from the Elector’s ordered strategy in order to do so.

Heinrich von Kleist’s play (premièred posthumously in 1821) dramatised many of the crises felt by its author, in particular the clash between personal desires and ideals and one’s equally sacred duties. Here, Charlie Cox as the Prince candidly admits to a terror of death by execution unlike any he faced on the battlefield, and his beloved Natalia (Sonya Cassidy) argues passionately with the Elector that mercy would follow a higher law than that of the fatherland. But McDiarmid’s Elector never wavers: even when offering the prince an apparent reprieve and when facing down a near-mutiny by virtually his entire officer corps, he runs from mumbling through biting sarcastically to outright explosion and, in Jonathan Munby’s excellent production,  never loses the whip hand.

Which, I’m afraid, is my main criticism. I admire Dennis Kelly immensely as a writer, and his version of the text here is strong and modern without being modish... Until the ending. I have simply had enough of “new versions” of plays that turn the original endings through 180 degrees. If you don’t believe in what the original playwright was saying, why bother with their work? If you do believe, why distort it? The dream/reality ambiguities of the original, and our own bleaker 21st-century outlook, are no excuses for what is a far greater act of betrayal than that of which the Prince himself is accused.

Written for the Financial Times.