There is something funny about Jonathan Lynn's serious play. It is set against a giant map of wartime France that, with a few advancing swastikas, could be used for the opening credits of Dad's Army. And, in his main protagonists, the Yes Minister writer might have come up with two characters that would make the oddest couple for a sitcom, were they not so steeped in the bloody history of their time.

Funnier still, Laurence Fox and Tom Conti do find comedy in the relationship between the two. In Fox's portrayal, Charles de Gaulle is a socially inept intellectual with no sense of humour. The leader of wartime Free France comes across like a high-functioning Asperger's victim, while his elderly mentor, Philippe Pétain, is played by the twinkly eyed Conti with stacks of avuncular charm.

"Is that a joke?" almost becomes a de Gaulle catchphrase, so lacking is this serious soldier's ability to spot a gag. Without this strain, Lynn's play - which he also directs - might have been an awfully dry affair.

We first encounter Pétain in his cell during his trial for treason. The leader of Vichy France and the inventor of the ineffective Maginot line, designed to protect France from German invasion (it's all helpfully marked out on the giant map) is waiting to see if his one-time friend de Gaulle will have him executed. This becomes an oddly deployed dramatic vehicle in the sense that, after Pétain establishes himself as the play's narrator, de Gaulle also muscles in on the job, leaving us in some doubt as to whose story we are watching.

More problematically, the set-up threatens to make this history drama feel awfully old fashioned. The biographical memory play is a hoary old thing. And once Pétain casts his mind back to the day the 23-year-old de Gaulle joined his regiment during the First World War, brace yourself for leaden dialogue crammed with expositional detail. Except nothing leaden comes. What emerges is a genuinely instructive, entreatingly told account of the Second World War as seen from a rare perspective.

Lynn persuasively argues that France's choices - to collaborate with, or fight Hitler - were bound up in the personal character of these two titans of French and indeed European history. And although modern relevance is an overrated virtue (a good story, well told is always relevant) the play works well as a reminder of what a fractured Europe looked like before the EU came along. (Odd that the "stay-in" campaigners rarely mention the war, though perfectly understandable that the Brexit lot don't.)

Where the play feels less sure-footed is where it appears to have accentuated the character traits of Pétain and de Gaulle for comedic and dramatic effect. This is especially conspicuous in the case of Pétain, who is depicted here as somewhat guilt-ridden over his decision to hand Vichy France's Jews to the cattle trucks bound for the East.

It is hard to reconcile Conti's seemingly warm-hearted humanist with that man, and also with an earlier moment, when as General de Gaulle punishes his own soldiers by having them thrown, with hands bound, into a no-man's-land trench to die.

Still, in every other way, the evening is completely solid. The dialogue is sharp; historically, it covers an enormous amount of ground without ever making you feel as if you have wandered into a lecture; and it is also terrifically acted (aside from the reservations about Pétain). Now, for that sitcom version.

Scene One

Sometime between World War One and Two, de Gaulle and Pétain's living room. De Gaulle walks in wearing his coat and looks with contempt at his flat-mate Pétain who is asleep with his feet on the table...