Good Omens series two – have David Tennant and Michael Sheen really only been a double act since 2019?

Sheen and Tennant, Tennant and Sheen. David Tennant and Michael Sheen’s double act is so well honed they parody it in BBC meta-comedy Staged. It feels as if they have been together for ever, but their on-screen partnership only dates back to 2019 and the first season of Good Omens.

Fans of the 1990 novel by Neil Gaiman and the late Terry Pratchett waited decades for a television take on the angel Aziraphale and the demon Crowley, working together to avert Armageddon in a world where heaven and hell are petty bureaucracies and the universe’s strongest force is flawed humanity. With Gaiman in charge of the series, the book’s vision had been rendered well enough, but all the magic was in the casting of two lead actors with similar sensibilities – a swaggering mischief built on sharp consonants and glinting intellect.

For season two there is no more book to dramatise, so the makers are free to play to series one’s strengths. Good Omens 2 is more the Tennant and Sheen Show than ever. If it’s not sure what else it is, perhaps that doesn’t matter.

Expanding on the episode that recounted the whole history of the world as background for Aziraphale (Sheen) and Crowley’s (Tennant) unlikely companionship, season two sends them on self-contained flashback adventures – these “minisodes” are woven into the regular action but have been farmed out to different writers, separately credited. In one instalment, Az and Crow are in the Land of Uz, plotting to make Job’s punishment by God a bit less over-the-top; in the next, they pitch up in Edinburgh in 1827 – Burke and Hare’s stamping ground – to wrestle with the ethics of graverobbing.

The fussy angel and remorseless demon as attracted opposites, learning to love the other’s extremes during an eternity spent together, remains a nice idea, and there’s a sneaky thrill in seeing more than one new acquaintance assume that Aziraphale and Crowley are a couple. Plus, aside from showcasing the grubby lushness of the historical set design, these detours are a mine of fan-pleasing Easter eggs. The identity of the actor playing Job is an amusing reveal if, like most of Good Omens’ audience, you have a strong interest in Tennant personally, while the minisode set in 1941 during the Blitz is a full League of Gentlemen reunion, co-scripted by Jeremy Dyson, with Steve Pemberton and Mark Gatiss appearing as Nazis, alongside Reece Shearsmith as an embittered administrator trying to weasel himself into a cushy management role in hell.

The linking present-day narrative is that the archangel Gabriel (Jon Hamm) has appeared on Earth and presented himself at the bookshop that serves as Aziraphale’s terrestrial cover story, but in the form of an amnesiac human who has no idea why he is there. The problem is, nor do we: the significance and mechanics of the story remain unclear as Hamm, previously one of the strongest supporting characters, now has to do his best with a basic affable-ignoramus role.

It’s bad news when the season’s main story prompts a bored sigh every time it resumes and some of the side plots are over the line between cleverly imaginative and lazily smug. On the colourfully retro, Paddington-ish cartoon of an English street where Aziraphale’s bookstore stands, he and Crowley are obliged – for plotting purposes – to intervene as meek record-shop owner Maggie (Maggie Service) woos spiky coffee-shop proprietor Nina (Nina Sosanya). The show knows it’s delivering shamelessly cheesy romcom pleasures: as he hatches a scheme to manipulate these unsophisticated mortals into falling in love, Crowley admits his plan is stolen from a Richard Curtis film.

Such showboating accentuates the feeling that Gaiman – who says this new season draws on a conversation he and Pratchett had in 1989 about a second book – didn’t quite know what to do with the recommission. In the hunt for fresh ideas he now shares his main-writer credit, too, and the name of the new recruit will make connoisseurs of British comedy pay attention: John Finnemore.

Finnemore rarely works in television, but his long-running Radio 4 sketch series Souvenir Programme is an appropriate calling card. That show delights in dusting off beloved cultural artefacts from bygone analogue eras and, via ruthlessly precise comic writing, teasing out a twist of absurdity, creating a sort of pedantic delirium. He is well suited to this show’s comfy Bakelite aesthetic, with punchlines referencing feather dusters and eccles cakes, and his voice is often audible, such as when Crowley recognises the name Jane Austen: “Brains behind the 1810 Clerkenwell diamond robbery, brandy supplier, master spy. What a piece of work … she wrote books [as well]?! Hm. Bit of a dark horse.”

Tennant gives lines like that the full tooth-baring, hip-snaking treatment. If you thought he and Sheen were a bit much before, they are much too much now.

• Good Omens series two is on Amazon Prime.