The new British movie “The Duke” may not change the world but in its unassuming, pleasant way it just might motivate moviegoers to become more active in their communities and/or get more involved in politics. 

Based on a true story, the account of a modest family’s brush with high art, economics, and the law inspires both righteousness and bonhomie.

Set in early 1960s England, the movie begins by introducing us to middle-aged Kempton Bunton (Jim Broadbent) as he toils away at his typewriter in a small home in Newcastle and his wife Dorothy (Helen Mirren) as she scrubs a fireplace as a housekeeper in a high-toned household. Right from the start, work is emphasized, and though it becomes clear that the plays Kempton writes don’t ever get produced, he’s still shown plying his craft.

We soon find out that Kempton is a bit of a rebel, as he refuses to pay a television license fee for accessing the BBC (a British law that’s still around today), much to his wife’s disapproval and his son’s encouragement. In the first 15 minutes or so, there are discussions of taxes, voting rights, and cultural elitism. What a difference from Hollywood movies, in which actual work, talk of economics, and other relevant issues are rarely portrayed.

After a short stint in jail for not paying the TV tax, Kempton takes a job as a taxi driver even while remaining passionate about abolishing the fee for pensioners and war veterans. His crusade takes him to London, and this is when the movie builds up some steam. 

Also in London, at the National Gallery, is a 19th century painting of the Duke of Wellington by the Spanish painter Goya. The portrait had been recently purchased for a pretty penny by the British government in order that it stay in the country. Kempton is incensed by what he deems to be a wasteful expenditure — and decides to steal it.

If all this sounds like a somewhat dour, kitchen sink English drama, the kind that was popular at the same time the movie is set, you’ll be happy to hear that it’s not. “The Duke” has a sprightly style, snappy music, and an efficient script with some genuinely witty lines. 

Director Roger Mitchell, who died last year, employs an irreverent tone similar to some of fellow countryman Stephen Frears’s films, such as “My Beautiful Laundrette,” “Philomena,” and “The Grifters.” As can be expected of the director of “Notting Hill,” Mitchell lays on the sentiment a bit thicker than Mr. Frears, especially in the later courtroom scenes where chuffed crowd reactions distract from the overall message.

Another element — one that feels shoehorned in — is an exploration of grief and family tragedy, possibly to add some subtext to the proceedings. Regardless of whether it’s true to life, the filmmakers never integrate these themes successfully, especially in the movie’s lumpy middle. Thankfully, a third act twist arrives that livens things up a bit.

The acting by the two leads matches their reputations as two of cinema’s thespian titans. 

Jim Broadbent plays an “everyman” with the lightest of touches, never overdoing the humble pride of Kempton nor over-emphasizing his anger. Helen Mirren takes what is almost a thankless role — the long-aggrieved and haranguing wife — and does some fantastic character work. The role can be seen as a low-rent variation of her Oscar-winning performance in “The Crown” (also by Mr. Frears), an association the movie acknowledges at one meta-point.

In the end, viewers may not remember much about the family’s problems or learn much about the stolen painting (“It’s not very good,” is Kempton’s assessment), but his rousing speech about humanity’s inherent goodness and interconnectedness near the movie’s end could stay front of mind for a while. And if, afterward, viewers get talking about issues like jobs, taxes, and voting rights, then the movie has accomplished more than most.