Lynn's play focuses on Pétain and de Gaulle's relationship. A national hero of the Great War, Pétain was mentor and elder statesman to the much younger academic soldier, de Gaulle.
But it was a relationship which ended up being riven by history, with Pétain's antisemitic Vichy government on one side and de Gaulle's Free French on the other. And it was a friendship that emphatically ended when de Gaulle tried Pétain for treason after the Second World War. It is a story through which Lynn explores the nature of patriotism.
"They were both patriotic Frenchmen," he says. "I have my doubts about the uses of patriotism. I think it was Shaw who said 'patriotism is when I believe my country is better than your country because I was born in my country'.
''De Gaulle is a hero. He was arguably the greatest of the Allied leaders during World War Two. He fled from France in 1940 when he was an acting brigadier, got into Britain and started the Free French in the teeth of apathy - if apathy has teeth."
It is a caveat that could easily have been said by the professionally pedantic Bernard in Yes, Minister and Yes, Prime Minister, the show that, to Lynn's apparent surprise, is still as relevant as it was in Thatcher's day when the series was first aired.
"I'm amazed that it doesn't seem to have dated. Occasionally, I see an episode repeated and the same things happen in the same way.
''So, yes, I'm very surprised by that. We wrote an episode of Yes, Prime Minister in which a character based on Solly Zuckerman, chief defence adviser at the time, explained why Trident was not necessary. Ah yes, the episode that revealed that we don't have a nuclear deterrent because of the Russians, but because of the French.
"A general told me that. Trident is a status symbol. People seem to think it's a left-wing position because Jeremy Corbyn holds it. But Enoch Powell said there was no point in having an independent deterrent. It's not a left-wing position that we shouldn't waste all that money on a weapon we will never use. It's a perfectly sensible position."
For the past three years, Lynn has lived with his wife in New York to be closer to their grandchildren. He moved there from LA where he directed a string of Hollywood comedies, often staring A-list names.
The best of these is probably My Cousin Vinny (1990), starring Joe Pesci. "It's a serious film, an anti-capital punishment film," says Lynn, "although I've always thought of it more as a film about untapped talent. Pesci is a loser personal-injury lawyer whose ability only emerges when he finds a cause worth fighting for. Up until then, Vinny is a nobody.
"Inevitably, being British, I emphasised class," says Lynn. Being British also gives him a perspective on modern America, a country he describes as "remarkable and terrible." I wonder if there could ever be a show called Yes, Mr President, perhaps starring someone rather like Donald Trump?
"There is nothing to say. He's just an out-of-control television personality," says Lynn, even though he then has plenty to say about the presidential hopeful. "I think Trump has fascist tendencies, I think he's a racist and a bully. But I think he is slightly less dangerous than all the other Republican candidates."
Really? "Yes, because I don't think he's doctrinaire. The others are all evangelicals, I think, and that's worse." Lynn adds that he believes some of the other Republican candidates come across as racist and do not believe in women having any rights. He goes on: "Trump has no serious policy thoughts. I think he's deranged and deluded. But not nearly so scary as the other candidates."
Perhaps, like Pétain, Trump is a misguided patriot. "Patriotism is a useless concept," says Lynn. And then, a little mischievously, I ask him if he is patriotic. The question seems to take him by surprise.
"By default. I'm not religious but if someone says to me, 'Are you Jewish?' I say 'Yes,' because I'm not prepared to say I'm not. So by the same token I'm not going to say I'm not patriotic." But he's not quite satisfied with that answer and later takes the trouble to write to me with a more nuanced version:
"If you were asking if I love Britain, I do. If patriotism means love of one's country, then I am indeed patriotic. If Britain were under attack (as France is in my play and as Britain was in 1940) I would be even more so.
"But I'm cautious because, to many people, patriotism implies a nationalism that involves a suspicion, contempt or hatred of foreigners and foreign countries. Donald Trump's or Ted Cruz's version of patriotism, about which I hear a great deal too much when I'm in America, is something I'm not keen on at all."
Then he adds, "I hope that clarifies my view." Which, of course, it does.
