Olivia Colman will narrate the film, with Matt Smith (The Crown) providing the voice of the hero, Superworm. They will be joined by Rob Brydon (Gavin & Stacey) as the Crow, and Patricia Allison (Sex Education) as Butterfly, with the announcement of other cast members later in the year.
The new cast members will guest feature as suspects in the first film of the Bath-based detective drama series, currently filming, alongside leads Jason Watkins and Tala Gouveia.
Gouveia and Watkins will reprise their roles as the unlikely pairing of the gutsy DCI McDonald and the humble DS Dodds.
James Murray also returns as Chief Superintendent Houseman, handing McDonald and Dodds three new murder mysteries to solve. Lily Sacofsky joins as DC Milena Pachiorkowski.
The new six-part series follows Brydon and Coogan as their fictionalised characters road trip around Greece on the hunt for more foodie adventures.
The pair debate about tragedy, comedy, myth and history, as they sample traditional Greek cuisine while travelling from one beautiful spot to another, which includes Hydra, Athens, Assos and Plyos.
Directed by Michael Winterbottom and produced by Revolution Films, the new series follows on from The Trip to Spain, which saw Brydon and Coogan travel from Getaria to Malaga.