It hasn’t always been this hot. The shoot started in the Redcliffe Caves in Bristol in April, in considerably damper conditions, and will go on until October. But for now, it is a hot and motley collection of Welsh extras who gather in the BBC canteen, incongruously tapping away on iPads and smartphones while dirtied up in Atlantean sandals and smocks.

Atlantis – or ATLANTIS, as the rather exclamatory press pack refers to it – is intended to be the next big thing: executive produced by the team behind Merlin, Julian Murphy and Johnny Capps, and created by Misfits showrunner Howard Overman, the production pedigree is impeccable.

There’s no denying the commitment, and the money, the BBC have invested in the show. The sprawling warehouse that is home to the sets and production base is so big that some members of the crew navigate it on Segways and bicycles. And there’s secrecy too. We’re forbidden even from tweeting that we’re here.

A glance at the photo gallery of cast members gives tantalising clues as to some of the actors who will be appearing across the series: Lucy Cohu, Gemma Jones, Will Merrick and CultBox favourite, Donald Sumpter. But, armed with our Bumper Book of Myths and Legends, it’s the character names that intrigue the most: Medusa, Tiresias, Jocasta…

Talking to the show’s creators, it is clear that Atlantis is going to be about more than just one very soggy city. It’s a chance to take a pick’n’mix approach to all the Greek myths, with one notable pantheon of absentees. ‘You never see the Gods,’ Murphy and Capps tell us – though their influence is all around.

Purists may not like the way different stories and characters collide, but the playful wit of the approach is partly the point – and is, in any case, true to the spirit of how the original stories evolved. Classical scholars advise on the show – and love it, according to Murphy and Capps. ‘The reach of these shows,’ they assert, ‘is more likely to draw people to Greek mythology than it is ever to put people off.’ But it’s in the set design that the attention to detail and research is most evident.

Bulls, given that we are at the court of King Minos, are inevitably everywhere: the first episode is titled ‘The Earth Bull’. But if we thought that the production team would hold back their trump card of the Minotaur until late in the thirteen-part season, we were wrong. He’s one of the standouts of Episode 1.

Scale – of the visuals and of the storytelling – is the one thing everyone is talking about. A three-week location shoot in Morocco has just been completed, and the sets have been designed to take into account the CGI that will transform a dusty corner of a Welsh warehouse into the Temple of Poseidon. Paul Cripps, the production designer, talks lovingly of the influence of Ray Harryhausen’s work on him growing up.

But there’s plenty of talent in front of the camera too, and here, the production team have repeated the Merlin formula of foregrounding new talent alongside established British character actors.

At its heart, it’s clear that Atlantis is a story of buddy bonding, and front and centre are the triumvirate of Jack Donnelly as Jason, Robert Emms as Pythagoras – yes, him of the triangles – and Mark Addy as a Hercules who, in the words of the producers, is much more like Falstaff than the Hercules of legend.

As the man who gets to go on the hero’s quest, Donnelly is new to the leading man role. His last television part before auditioning for Atlantis was as a man in a rabbit mask on Misfits. But as he chats to us in interview – recounting a rather gory story of a trip to A and E, and blithely telling us a spoiler for Episode 1 – it’s clear that he’s no diva and that the bromance with Addy and Emms continues off-set as well as on.

Goodwill, in fact, and enthusiasm for the show is all around us. Murphy and Capps are understandably hesitant to talk too much about a long-term plan; but there is acknowledgement of the five-year run of Merlin, and recognition that, with the entirety of the Greek myths to draw on, there is no shortage of source material to sustain the programme in future years.

Whether the city of Atlantis gets flooded sooner or later remains to be seen. But on the evidence of the ambition of the production, one thing is clear: Poseidon-willing, the BBC are in it for the long haul.

Atlantis begins on Saturday 28 September on BBC One.

> Read our spoiler-free review of the first episode.

Watch the Atlantis launch trailer…

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