One gets the impression that the Brits regard Terence Rattigan’s “The Winslow Boy,” as a play, a film, a TV movie or radio drama, with the same warm esteem that Americans regard Frank Capra’s “Mr. Smith Goes to Washington.” One does.

The subject, an entertaining and uplifting drama about “a little” legal case from the Edwardian Era that referenced all the way back to ancient and sacred Magna Carta about a fundamental human (and English/British) right, it struck a chord back in 1946 when Terence Rattigan brought it to the stage. The many productions of it that have followed — films and broadcasts included — underscore this.

Based on a real case that Rattigan fictionalized, and that was further tinkered with when he, director Anthony Asquith and co-adaptor Anatole de Grunwald prepared it for the screen, it amazes in the ways it works and the obstacles that Rattigan built into it that work against it.

Consider — the two biggest dramatic moments in this case and its trial take place offstage/off-camera. They’re described by other characters who witnessed them or read accounts of those events from the newspapers. That’s daring.

It should have driven Asquith (“Pygmalion,” “The Browning Version,” “The Millionairess”) a bit batty, knowing they wouldn’t be “opening up” the play for the screen by filling those two admittedly-calculated holes.

But the film, starring some of the formidable talents of the pre-war to post-war British cinema, including Robert Donat, Cedric Hardwicke, Francis L. Sullivan, Basil Radford and Marie Lohr, has a timeless lump in the throat “always be an England” appeal. Thanks to generous helpings of music hall visits and dancing to music on the home Victrola, the real attempts at “opening the play up,” it plays like a pre-“Downton Abbey” snapshot of that era, the years just before and during World War I.

An upper middle class banker (Hardwicke) comes home to his first evening as a retired banker only to discover that his youngest son, Ronnie (Neil North) has been expelled from school.

But this wasn’t just any school. Ronnie has been kicked out of the Royal Naval College in Osborne, a boy of twelve — these were the last years when the Royal Navy enlisted children that young as “Young Gentlemen” — accused of stealing. Ronnie is marked for life at 12, and father Arthur is understandably peeved.

A quick “If you tell me a lie, I shall know it” test fixes father’s course of action. He goes to the college, and getting no satisfaction — they won’t even give him the evidence they used to summarily dismiss and disgrace Ronnie — Arthur starts the long process of taking the Royal Navy and by extension “The King” to court.

His suffragette daughter (Margaret Leighton) gets it, even as the case creates notoriety that might spoil her marriage hopes. Oxford-student son Dickie (Jack Watling) seems unconcerned, not really grasping the gravity of what has been done and how and what the family is about to put itself through. Mother Grace (Marie Lohr) wonders if this all isn’t getting out of hand.

Because Arthur gets his solicitor (Basil Radford) to try and get permission to sue. And when that isn’t granted he talks the most famous barrister in Britain, Sir Robert Morton (Oscar-winner Donat of “Goodbye, Mr. Chips”) into taking the case.

Morton is polished, accomplished, cool and forbidding. He rubs daughter Katherine the wrong way before she even meets him. And the way he questions the boy — briskly, in evening clothes, ready to dash off to a posh dinner any second — puts the entire family off.

It’s an interrogation and the kid breaks down.

But the imperious legal eagle takes the case, which he realizes will be tried not just in court, but in the court of public opinion and even in Parliament. When you’re contesting the idea that The King must allow himself to be sued, but “the King is never wrong,” via taking on the King’s Royal Navy and the Admiralty “lords” that run it, everybody will have a say.

” I have every intention of applying a slight but decisive spur to the first lord’s posterior in the House of Commons!”

The film version has slice-of-life moments where the Winslows visit London music halls to be entertained by real-life veterans of that 1912-1915 world — Cyril Ritchard and Stanley Holloway (later Eliza Doolitte’s Dad in “My Fair Lady”) were still living and doing their acts in the late 1940s.

Part of those acts was a freeform style of singing not unrelated to rap, turning notorious current events shouted out from the audience — National Health, Women’s Suffrage and “The Winslow Boy” — into verses of songs they’d make up on the spot.

The various debate and trial scenes with Donat are what make the picture, as he does a grand job of grandstanding and thundering through lines of accusation, protest and pleas that the attorney general (Francis L. Sullivan, famed for his turns in “Oliver Twist” and “Great Expectations”) allow a “petition of right” against the king be allowed to be brought to the House of Commons for trial.

“Let right be done,” was the traditional line the attorney general would use in allowing such a petition, a line Morton repeats often and to great effect, even as the attorney general resists using it at all costs.

In resetting the story to fall in the early years of World War I, with Europe in crisis “and barricades going up in Dublin,” the government wasn’t interested in being criticized. At all. Much less sued.

The arcana of English law is interesting, but this picture endures thanks to the performances and the blend of seriousness and deliciously light banter. A servant chatters on and on, Dickie keeps sticking his foot in his mouth and Morton and Katherine exchange barbs — he’s a titled and entitled sexist — that delight through the ages.

“Still pursuing your feminist activities, Miss Winslow?”

“Oh yes.”

“Pity. It’s a lost cause.“

“How little you know women, Sir Robert.”

That sparkle and the lump-in-the-throat nobility of the cause and the arguments for it make “The Winslow Boy” endure in Brittania. The rest of film fandom can only wonder how Frank Capra would have staged the two big dramatic moments Rattigan omitted and never added, even when he had movie production money to indulge in it.

Rating: “approved”

Cast: Robert Donat, Cedric Hardwicke, Margaret Leighton, Basil Radford, Jack Watling, Marie Lohr, Kathleen Harrison. Francis L. Sullivan and Neil North.

Credits: Directed by Anthony Asquith, scripted by Terence Rattigan and Anatole de Grunwald, based on Ratigan’s play. A British Lion/Eagle Lion release on Tubi, Amazon, etc.

Running time: 1:53