As we might expect, The Trip to Greece starts with a bad joke. Surveying the ruins of Troy, Steve Coogan reveals that he had a bad dream last night. Quick as a flash, Rob Brydon asks: “Was it a portent? I had a poor tent once. No groundsheet”. Coogan harrumphs, walks off, Brydon trailing after him. So far, so familiar.

It’s the show in a nutshell, and we are immediately on solid ground. Since its first series a decade ago – a brief zigzag across the Lake District, interspersed with pubs and gloomy landscapes – Michael Winterbottom’s creation has remained pretty much unchanged; the journeys may get longer, the scenery more breathtaking, but the essential elements remain the same, as the ur-Coogan and ur-Brydon trade impressions, insults and occasionally intimacies over various plates of delicious food, all in the name of an Observer column.

Once again, we encounter the two tracing the steps of a great literary journey. This time they are in the Mediterranean, so naturally they have set their sights on the big one, the original – the Odyssey of Homer, the ten-year voyage of the eponymous hero back to his native Ithaca. Of course, the journey isn’t simply a route for them to follow, but also an interpretative frame upon which Winterbottom can shape the wandering of his own heroes through any number of ironic parallels or indeed poorly timed impressions.

Across the four seasons, a variety of literary models have been employed; first Coogan and Byron were Wordsworth and Coleridge, grumpily stomping around the Lake District; they then traipsed through Italy as Byron and Shelley; and latterly we left them in Andalusian Spain, mimicking the quest of Cervantes’ Don Quixote and his faithful retainer Sancho Panza. As the show has developed, the analogies have gained more weight as a conceit, and the Odyssey continues this tradition.

As a model, it is curiously apt. The method of fixing content to form or genre, as Winterbottom has done throughout the show, switching through modes to find the best fit, is for one thing a standard trope of classical poetry; we might think of the opening to Ovid’s two most famous works, Amores and Metamorphoses, both of which dramatise the selection of the genre in question – elegy or epic – as a programmatic statement on the nature of the work to come. Winterbottom is working in the same tradition. By virtue of the model chosen, we know that nostos, homecoming, will be the driving force behind the series’ emotional arc.

Beyond that, the Odyssey is in a sense the first metatextual epic; like Winterbottom, it is enamoured with the possibilities and problems of the act of storytelling itself, which permeates the poem from start to finish. Odysseus with the Phaeacians, the song of the Sirens, Menelaus and Telemachus, Odysseus with Penelope: throughout the poem, characters are constantly telling each other stories which imitate the one that they themselves are in. His gift with words is arguably Odysseus’ great talent as a hero: not for nothing does his climactic act of stringing the great bow to prove his identity neatly recall the act of stringing a lyre.

The Odyssey stands in relation to the Iliad much as the two reflect the respective elements in which the majority of their action takes place. The Iliad is solid, whole and compact, like the scorched earth of the Trojan plain, whilst the Odyssey is slippery, shimmering and transitory, like the seas which its hero must cross to get home. This instability of interpretation is innate to The Trip; throughout, although we know that we are watching Coogan and Brydon play versions of themselves, they do so with such ease and naturalism that the illusion is constantly pulled at, and we find ourselves guessing which bits are real and which not.

Coogan remains the emotional pivot of the show, and in this series it is Coogan who assumes the character of Odysseus. Even his fundamental insistence that he is more than just a comic actor – “Award-winning actor, producer and writer”, he snaps at Brydon at one point, is a winking play on Odysseus’ fundamental epithet, polytropos – of many wiles.

In all four seasons of The Trip, ur-Coogan’s concerns have been the closest thing to plot points the show has had. There is his quest for respect as a dramatic actor, his search for love – of both self and another – and now, of course, his search for home. Here again, the Odyssey is the perfect foil; robbed by circumstances of his triumphant return, we leave him out-of-place and uncomfortable in his ex-wife’s house, while Brydon cavorts with his own wife on Ithaca.

Coogan’s emotional experience is at once in stark contrast with the conclusion of the Odyssey, and also very attuned to its ambiguity. In Book 11 of the poem, the blind seer Tieresias tells Odysseus that his journey will only be finished when he comes to a land where the people know nothing of the sea, where they mistake his oar for a winnowing fan for the harvest. This cannot be sea-girt Ithaca; and so we know that, like Coogan, Odysseus has not found his nostos – a pathos magnificently misread by Tennyson in his triumphalist variation on the post-Odyssey tradition, Ulysses.

Just, then, as we know that Odysseus has not reached home, so too Coogan. His journey, it seems, is not yet done. It’s this truth that sets the overwhelming mood of the piece: melancholy. Not, perhaps, the melancholy of the Italian series, all faded palazzos and post-imperial decline, but something quieter, more fitted to the wooded dells of the Ionian islands.

Despite this, the show is unafraid to skewer its protagonists, as one sequence from the opening episode encapsulates perfectly. Landing on Lesbos, Coogan is accosted by an extra from a former production, who asks them to take him to the Moria refugee camp, one of the largest and most notorious such settlements on the Aegean islands. Coogan agrees, despite Brydon’s obvious discomfort, because “that’s what odysseys are for”. A human tragedy of genuinely epic proportions becomes a detour on a very expensive culinary jaunt, a tension hammered home by the juxtaposition of Coogan’s ridiculously expensive Range Rover and the camp’s gates. In its undemonstrative way it is an extremely brave and effective choice, much more so arguably than the out-an-out satire of Coogan’s latest feature, Greed.

By its nature, The Trip is an open-ended show. New seasons arrive suddenly and sporadically, and it could finish at any time. Equally, its essential elements are so minimal that one can also conceive of a new season every three or four years until one of the three main collaborators gets bored. Considering how much remains exactly the same each time – the set-up, the repertoire of impressions, the constant bickering – it is remarkable how much the three have managed to mine from the set-up thus far.

Perhaps, as they age we will get one last great variation on the theme. Lear and his fool upon the heath seems like the ultimate model: the vain, angry king and his far wiser jester. It’s unclear exactly where they would get the food, but then, it’s never really been about the food anyway.