If it weren’t for stars Terence Stamp and Vanessa Redgrave, “Unfinished Song”—originally titled “Song for Marion”—would be pure sentimental claptrap. With them it’s still that, but they’re such formidable personalities that they almost make it worth watching from sheer force of will.

Redgrave plays Marion, the angelic, terminally ill wife of gruff retiree Arthur (Stamp). Though frail, she’s devoted to singing in the neighborhood’s chorus of elderly folk that their ebullient young director Elizabeth (Gemma Arterton) has dubbed the OAPs, or Old Age Pensioners. Since the normally brusque Arthur is equally devoted to her, he takes her to the group’s rehearsals, though he thinks the whole business a lot of nonsense and waits outside, smoking, to escort her home afterward.

Elizabeth has also decided to enroll the OAPs in a choral contest for which they learn a new repertoire—predictably, a bunch of rock songs that play on the cuteness factor of oldsters singing them. At the outdoor recital where they’ll be judged as to whether they’ll be counted among the finalists—and go on to the concluding round—Marion is also given a solo, a slow rendition of Cyndi Lauper’s “True Colors,” which also serves as a valedictory statement of her love for Arthur, who stands morosely among the crowd of well-wishers. Naturally the OAPs will advance to the final round.

But it will be without Marion, who expires shortly thereafter, to Arthur’s enormous pain. Her death doesn’t even manage to bring the taciturn widower back to an emotional connection with his estranged son James (Christopher Eccleston), a single dad to the adorable Jennifer (Orla Hill), who’s angry that Arthur showed no affection for him over the years. But it does lead Arthur to approach Elizabeth about joining the OAPs, revealing a fine voice that will lead to his being assigned a solo in the finals, a number that will serve as a posthumous love letter to his beloved Marion.

Of course, that’s the stripped-down version of the scenario that writer-director Paul Andrew Williams has concocted. There are complications that arise in the last act to threaten the group’s participation in the concluding contest, of course. And throughout there are moments designed to highlight the darling character of the other chorus members, who are frankly employed as ever-so-cute props in a virtual paean to the lovability of oldsters. There’s even an odd, intrusive episode in which Elizabeth approaches Arthur for comfort after she’s dumped by her boyfriend. (Happily, that isn’t taken very far.) And it goes without saying that Arthur and James enjoy a rapprochement.

It’s all terribly predictable (even if a connection between James and Elizabeth, which one might have expected, doesn’t occur)—a manipulative assemblage of tear-jerking clichés that doesn’t so much strain credulity as shatter it completely. But it has Stamp and Redgrave, who play Marion and Arthur with such conviction that one almost buys into it. She brings her patented sense of ethereal fragility to the mix, and he’s fine as the sullen, taciturn man who can show love only to her, until she’s gone—at which point he begins to flower, even if only inwardly. It’s a perfect example of how trite, second-rate material can be elevated by a couple of canny veterans whom an audience will automatically be rooting for. And both milk their solos for all they’re worth—which is quite a lot.

Otherwise “Unfinished Song” offers only meager rewards. Neither Arterton nor Eccleston brings much to the party, the supporting oldsters are mostly treated as comic caricatures, and in visual terms the picture is no better than average, with Carlos Catalan’s cinematography capturing the lower-middle-class British ambience but never evincing any imagination.

Older viewers may be moved by the saccharine contrivances of “Unfinished Song,” and everyone can appreciate the wealth of experience and expert timing the leads bring to these weakly-written characters. As an acting lesson, the picture has something to offer. But not much else.