“A United Kingdom” tells us the story of Ruth, a simple British office clerk who meets a black law student at a social mixer, completely unaware that it’s an historic meeting that will result in a marriage that will change their lives and African history — drawing the British parliament, South Africa and even Winston Churchill, into political conflicts.

Directed by Amma Asante, a former child actor and model, “United” is a true love story cum political thriller set in London and Africa in 1947.

Rosamund Pike, in a strong departure from her role in “Gone Girl,” spots Seretse Khama, (David Oyelowo, “Selma”) across a crowded, smoky room full of law students and their friends.

In order for director Asante to get to the big, meaty points, they fall in love on the spot and aware of inevitable trouble, spend a year or two hiding it before they marry.

It’s clear what problems and stress we’re going to see unpacked, even though we’re in England, without American “hanging” judges and Alabama sheriffs in tight white shirts.

Unlike the local strife played out in Jeff Nichols’ Virginia racial drama “Loving,” this romance will eventually rock the headlines on both sides of the Atlantic, even though today it’s vanished news.

Ruth’s father, British white to the core, is of course shocked and repelled, but her mother and sister (“Downton Abby’s” Laura Carmichael) being women, look for a solution.

The big surprise for Ruth comes when Seretse reveals that he’s about to become a king, chief actually, of Bechuanaland, now Botswana, in Africa. Surely more than Ruth bargained for. No rose covered picket fences here.

In a touching scene, Seretse gets down on his knee on a foggy bridge in London and proposes, while flocks of Londoners walk by. Imagine the same scene on that bridge in Selma.

In another scene, director Asante gives us a bit of a scare when the couple are attacked on a London side street by hooligans. After that the violence is mostly emotional and political.

The script is flawed here by British government officials involved who are purely unabashed stereotypical villains and anti-romantics, played by Tom Felton and Jack Davenport who, in another era would boast curled mustaches and be hissed and booed by audiences. They’re that corny.

The real story grows in intensity when our king-to-be takes his bride home to British protectorate Botswana, which when we see it, is not much more than a scattering of thatched huts, dusty streets, so barren that one wonders why the Brits would give a hoot about it.

Later we find that the Brits and an American company have a secret here. It’s important to add an unknown moment of political betrayal by Britain’s hero, Winston Churchill.

Arriving, Seretse and bride meet his uncle (Vusi Kunene) — a calmer, but still resolute opponent who, in place of Seretse’s deceased father, is the Regent assigned to keeping the throne warm for his nephew.

Wouldn’t you know that the locals turn up their collective noses at having a white queen sit next to their black king in what will become a political chess game.

“A United Kingdom” is well played by two excellent actors and, with a few flaws, a worthy back up cast.

Pike is simply a radiant and kindly Ruth, with eyes full of glowing naivete. She had me with her opening line: “Hello, I’m Ruth.”

Oyelowo, a proven actor in another political role, once again gets to deliver some powerful speeches and, for a change, some tender, sensitive love scenes.

Together, their chemistry makes a movie that’s bumpy and sugary, with some racial caricatures, much more enjoyable. This all comes, by the way, from Susan Williams’ book “Colour Bar,” and screenwriter Guy Hibbert (“Eye in the Sky”).

My thanks to director Asante for keeping it all to 100 minutes, and to Sam McCurdy’s camera that catches the dust, the heat and the love in Pike’s eyes.

J.P. Devine is a former stage and screen actor.