When I was offered the chance to review Dough, the first theatrical feature in what looks like 28 years from director John Goldschmidt, I initially declined. With my mother's health still poor, my free time remains restricted, and a quick read of the plot summary suggested that the film was going to play to the sort of well-worn formula that meant that I was going to be able to predict every major plot twist, including the ending. If that seems a little presumptuous on my part, try this for size.

Elderly and widowed Jewish baker Nat is struggling to keep his business afloat, particularly as Sam Cotton, the hard-nosed owner of a chain of local supermarkets, is determined to purchase the shop from its landlord, Joanna Silverman, and force Nat out. When Nat's assistant departs to take a job with Cotton, Nat starts looking for an apprentice and finds one in the shape of the initially reluctant Ayyash, a cash-strapped Muslim immigrant who lives with his mother in a squalid flat and has started dealing drugs in the hope of raising enough money to buy them both a better life. Then one day, a consignment of the cannabis Ayyash has been given to sell by hard-nosed drug dealer, Victor Gerrard, becomes inadvertently mixed into the bread dough. In no time at all, customers are lining up to buy this very special product, in the process turning the fortunes of the bakery around.

Now if that leaves you with no idea how the plot could possibly play out, then I'd skip a couple of paragraphs and watch a few more movies. It occurred to me immediately that certain things were likely to be a given here: that the relationship between Nat and Ayyash would initially be prickly but that as Ayyash learned his new trade, the bond between them would grow; that Nat would eventually discover the real reason for the increased sales and that the revelation would drive a serious wedge between him and Ayyash, probably at the point when their friendship was at its peak; that Victor would intervene in a way that would either threaten Ayyash's operation or Ayyash himself; that Cotton would work out what Ayyash is up to and use it to force Nat to sell up or move on; and that Nat and Ayyash would somehow overcome their differences to fight back against Cotton and save the bakery. All that just from reading a synopsis. What a horribly cynical bastard I've become.

Yet having made my decision, I gave the trailer a look and found myself wondering if I hadn't been a little rash. It was a charming sell, with beguiling performances and an engagingly unforced way with character comedy, so I agreed to watch and review the film after all. Twenty minutes in, I found myself marvelling at the skill of the trailer makers and becoming aware that my initial, pre-viewing assessment was probably going to be on the nose after all. Nowhere are the indicators more blatant than in scene in which we first meet Sam Cotton, played with a permanent air of contempt by the lovely Phil Davis, who concludes a brusque business call by pushing a toy car around the model of the multi-story car park he intends to replace the shop with like a gleefully malicious kid, and I could almost hear him thinking, "Yeah, big car park, lots of cars, lots of cash, brilliant!" For all the film's virtues – and I'll get to them in a minute – Cotton is like a bad guy from a Disney cartoon. You could, of course, say the same about drug-dealing hard man Victor Gerrard, but as a character he's given more depth and more screen time, and as played by a skin-headed Ian Hart, is a figure of convincing potential menace.

With almost every plot development relatively easy to predict, it's down to the lead characters and fine detail to lift the film above the level of a by-the-numbers comedy-drama, and herein lies its strength. It would have been all too easy for both Nat and Ayyash to be played as broad stereotypes, so it's to the considerable credit of director Goldschmidt and his two leading men that both are so rounded and grounded in reality, and their growing friendship and mutual respect thus rarely hits a false note, despite playing out by the narrative numbers. As Nat, the always impressive Jonathan Pryce is a constant delight, playing him as a grouchy elderly and cynical Jew without ever slipping into caricature, while Jerome Holder brings an instant likeability to Ayyash, a boy who is looking to deal drugs solely to raise the money to enable himself and his mother to move out of their appallingly run-down abode. That the men are at first mutually suspicious of each other is par for the course, but does at least make sense here. Nat's business is failing, he's lost his assistant to his arch enemy, and his lawyer son has no interest in taking over the business and believes Nat should sell up. He agrees to hire Ayyash on a trial basis only, doing so primarily because Ayyash's mother already works for him as a cleaner and all the other applicants for the job are clearly hopeless. Ayyash, meanwhile, has little interest in baking or getting up at 5am each day to work, and only accepts the post to appease his forceful mother and because Victor tells him that he needs to find a 'cover' job before he can start selling weed for him.

Pleasingly, race is almost never an issue here and the inevitable clash of religions proves to be no clash at all – Nat only realises that Ayyash is a Muslim when he discovers him praying in the shop before it opens, and after expressing his surprise he merely asks him to pray out back instead where he can't be seen by others. That Nat, who despite the assumptions of the bigoted Cotton is third generation British, openly accepts this Muslim immigrant into his workplace and eventually his home promotes a pleasing message of unity, and when his rabbi passes casual comment on Ayyash's religion and skin colour, Nat's response is to simply roll his eyes and walk smartly away. In that respect, it's a strength of the film that while Ayyash is at heart a good person, he's not exactly an innocent, although this does pave the way for the scenes of personal crisis, redemption and reconciliation so beloved of such stories. Nat's relationship with his widowed landlady Joanna Silverman (a bubbly Pauline Collins) also doesn't always play to expectations – she's clearly fond of him and is not shy of showing it, but is not quite doted enough to cancel what she regards as a favourable business deal with Cotton. In the end, it's the quieter moments involving either Nat or Ayyash or both that prove the most entrancing, as when Ayyash breaks off from his prayers to talk about his religion to Nat's wily young granddaughter Olivia (a winning performance from newcomer Melanie Freeman) and reassure her that her family really does care for her, or when Nat gets a taste for the hash-laced chocolate brownies that Ayyash has baked and presented to him and cheerfully recalls how he first started dating his late wife.

A word I've seen used more than once to describe the film is 'sweet', and it's a fitting adjective, in all that is good and not-so-good about what this implies. It's a film peppered with interesting characters and enjoyable scenes, has two hugely engaging performances at its centre and carries the sort of positive message about tolerance and understanding that we could do with more of in these increasingly bigoted times. It's just a shame all these fine elements have been packaged into a narrative whose structure feels drawn up from a well-worn, off-the-shelf template, one whose only real surprise is the decision to transform this low-key character drama into a caper movie for the climactic scene. It's still well worth seeing for the two lead performances and the developing relationship between Nat and Ayyash, and as an upbeat commercial for the joys of cooking with cannabis, it currently has no peer.

Dough is released in cinemas in the UK and Ireland on the 2nd June 2017.