When it comes to guarding the flame, there are few people more fastidious than Shelton “Hank” Williams III. Although he never met his grandfather (III’s father, Hank Williams, Jr., was only three years old when country icon Hiram “Hank” Williams died in the back seat of a car in West Virginia on his way to a gig on New Year’s Day, 1953), Hank III has been consistently outspoken about the way the country establishment treated the music’s biggest star. “Hank made history when he passed on,” Hank III told me in 2008, “and those that hated him all of a sudden started lovin’ him. But now it’s time to pay some respects.”

So if anyone was likely to find fault with the casting of the part of his grandfather in the forthcoming biopic I Saw the Light, it was going to be Hank III. And sure enough, once Tom Hiddleston was signed up, the combative grandson weighed in. It wasn’t that Hiddleston is English, it’s that he’s not a southerner; Matthew McConaughey would have been a better fit, Hank III wrote on his Facebook page. After footage surfaced last year of Hiddleston running through some Hank hits on stage with country singer Rodney Crowell, a consultant on the movie, Hank III criticised the lack of “soul or moan” in his vocal performance.

In the first clip from the film, which Hiddleston published through his Twitter account on Thursday, many of those justifiable concerns are addressed. His baptism of fire with Crowell last year clearly gave only a very preliminary draft of Hiddleston as Hank: that the actor was willing to try out in public what was still then very much a Hank Williams impersonation says more about his courage than it suggests about his potential to convince in the role.

The clip from the film is brief – we see Hiddleston singing as Williams for only 35 seconds – but it’s clear that he is more than up to the task. He certainly looks the part: suitable camera positioning and a solid job by the hair and make-up team get him some of the way there, but he’s got that thin-lipped half-smile – amused yet rueful, confident but brittle – which neither George Hamilton (Your Cheatin’

Heart, 1964) nor Sneezy Waters (1980 TV movie Hank Williams - The Show He Never Gave) managed to locate.

Just as impressive is the vocal performance. Gone is the slightly nervous sense of feeling out the voice that we heard in that first bash at Move It On Over with Crowell last year. Hank’s voice on record often sounds a bit reedier or thinner than Hiddleston does as he replicates that 1947 studio session, but part of that may be down to the limitations of the era’s audio technology. Tape of Williams talking suggests he had a deeper and more resonant tone than the records tended to capture, so if in Hiddleston’s performance we hear something a little more sonorous, it’s hard to argue that it’s inaccurate.

More importantly, this brief glimpse suggests that the British actor has done what he set out to do, and brought the essence of the man to the screen. Williams, who was only 29 when he died, tends to be seen as tragic icon first, master poet-musician second, flawed but very relatable man some considerable distance beyond that. We hear him sing and we know what happened next, so we read dread portent into every moan, hear intimations of mortality even in songs that overflow with life and vitality. Yet in the clip, Hiddleston is clearly trying to let us see Williams as a human being who lived a life, not as a walking ghost tracing a preordained path to his personal gallows.

It’s never going to be enough for Hank III – who has reiterated his belief that the film isn’t southern enough, though now seems to be directing his dissatisfaction at the choice of director (for him, Clint Eastwood would have been a better choice than Marc Abraham). But this first indication suggests that Hiddleston may have managed to give us a Hank Williams the rest of us can believe in.