LAST year, Tony Jordan experienced a spot of déjà vu. He was in Morocco. It was hot and dusty, and he was surrounded by actors wearing Middle Eastern sandals. It was, in fact, much like the stable scenes he had flown out to watch in his previous BBC1 Bible drama, The Nativity. Same filming area, same broadcaster, same surfeit of facial hair.

Only this time the characters were 2500 years older, and there was no baby Jesus. "There was a moment when I was at a table with the actors, and I suddenly thought to myself, 'I'm sitting with Noah and his kids, and we're having tea before he goes out to build his ark . . .'" He was assailed by a sense of awe. "It was a weird but moving moment."

More than four years have passed since Jordan's Nativity was shown on BBC1. Now, finally, he's back with a follow-up. The Ark is a feature-length drama about the Flood, starring the actor from Shameless, David Threlfall, as Noah, and Joanne Whalley (last seen as Catherine of Aragon in Wolf Hall) as his wife.

Like the previous work, it's a typically Jordan film: kitchen-sink modern in approach but traditional in setting. The characters use 2015 English but wear the swords-and-sandals garb of the standard biblical epic. There are dramatic embellishments - notably a son who threatens not to board the boat - yet the plot is broadly sympathetic to the account in Genesis.

If anything, in fact, The Ark strikes a more explicitly theistic tone than The Nativity. The film is dotted with conversations about the nature and existence of God, with Noah positioned as a lone voice of apologetics in a sea of atheism.

"Look," he says to his son at one point, "you can say I don't know [if God exists]. At least that's honest. But only an idiot would say, 'There is no God,' because, surely, you must first understand everything, and only an idiot would think that he did" (hat-tip Psalm 14.1).

In The Ark, Jordan is continuing a personal journey that began with The Nativity. A former market trader, who rose to become one of TV's leading scriptwriters, he started writing that drama without any belief in the biblical narrative. During the process, he completely changed his mind. "The only thing I know for sure is that the words I read as coming from Jesus Christ are the most truthful thing I have ever heard," he remarked at the time.

When The Nativity came out in 2010, and won some of the highest audience-appreciation ratings on record, the BBC gave Jordan virtual carte blanche for his next project. He said he had an idea for Noah; they commissioned it without even seeing a script. "Brave!" he laughs. Given the success of his first attempt, then, the only question is why it has taken until Holy Week 2015 to get the sequel.

Essentially, he sighs, it came down to finance. "Generally with these things you don't get enough money from your broadcaster, so you have to find a production partner. But finding partners for single dramas is difficult because everyone wants a series, they want volume. So we had to kind of hang around."

Ultimately, they found a backer in Up TV, a Christian-tilted US network that re-runs shows such as The Waltons, and Dr Quinn, Medicine Woman. Though by then, of course, Hollywood had found God, too. "There was the big Bible series, and then the announcement about the Russell Crowe film on Noah. So, as often happens in our industry, we suddenly found ourselves 'cool' and ahead of the game."

Ahead of the game or slightly outflanked, though? To be honest, Jordan admits, the Crowe news was a blow.

"I was gutted. We'd been around two or three years before them, I'd got really excited about retelling this story, and I had two million quid to do it. So to hear they were making this big Hollywood thing and spending something like $150m - I mean, it was a bit ridiculous."

He coped with his disappointment by refusing to read or watch anything about the film. "If anybody even brought it up, I told them to shut up." Basically, he says, he didn't want to lose his focus.

"The thing about my story is that [the Genesis narrative] was always about faith. We've turned it into a sort of Peppa Pig children's story that's all about a little boat with animals. Of course, it's about those things, too, but it's more about one man's faith in the face of everything else.

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"So I wanted to hold on to that. I was worried that if I heard about how they were doing this amazing flood sequence, I'd lose faith in what we were doing, and maybe feel that we should do the whole animal thing."

ACTUALLY, he needn't have fretted. Crowe's Noah was visually impressive, and scored decent box-office returns, but its spectacular deviations from the Bible left most Christians nonplussed. To take two examples: there were stone giants ("Watchers", loosely inspired by the Nephilim, apparently), and a nemesis, Tubal-Cain, who stowed away on the ark, post-deluge.

"If you want to make a science-fiction movie about rock people, fine - just don't call it Noah," Jordan snorts. He finally watched the film once his Ark was finished, and was delighted to find that he absolutely hated it. He found the ending "cod, cheap, nasty", and the execution terrible.

"Everything about it was bad. I laughed out loud in places, and I'm sure that wasn't the intention. They took the name 'Noah', took out everything from that story that meant anything, and turned it into Harry Potter. With rock people."

To Jordan's mind, the real drama in the Noah story isn't the spectacle, but the moral question that precedes it: what happens when an ordinary man receives a message no one wants to hear? He framed it in typically down-home terms. "I'm sure my wife and six kids love me, but if I started building a boat in the garden, and said God told me everyone was going to die, they'd get me committed."

In his research, he soon found a way to dramatise the question. The Qur'an's version of the story mentions a son who refuses to accept Noah's message. Jordan took that reference and expanded it into a character called Kenan (played by Nico Mirallegro), whose doubts provide a counterpoint to Noah's fatherly love and faithful conviction. "What's really handy with Kenan is that you're able to see what the other side looks like when you don't have faith."

Kenan's presence also lends emotional tension to the thorny theological problem at the heart of the story: namely, how does a loving God wipe every man and beast from the earth? And what would that feel like?

Noah rather ducked the issue by making Crowe's deity so inscrutable that he could almost have been a Norse god of war.

So how did Jordan deal with it? "Look, it's a struggle to do that stuff," he admits. In the script he found himself referring to it as a "cleansing", though that has tricky connotations. "The minute you say, 'I'm going to cleanse the earth,' it sounds a bit like ethnic cleansing."

Eventually he added an extra-textual rescue caveat - that people had the opportunity to join Noah in the ark, rather as Ninevites averted destruction by heeding Jonah's warnings. Ultimately, though, Jordan took God's rationale in Genesis 6-8 at face value.

"If we're being faithful to the source material, which I'm trying to be, then the people who died [may have been] given the opportunity to be saved. . . But it's like if you're a gardener, and you have a plant that's covered in disease, with one healthy shoot; it makes sense to cut off that shoot and replant it, and discard the rest. And discarding is tough, you know? People die. But is that any more wicked than anything man has done? No."

When it came to depicting the Flood, Jordan had a couple of aims in mind. "One thing I wanted was to feel the sense of God's power. In The Nativity, we captured that with a sequence where you saw the planets moving. I wanted to feel that power here, too, so my version has tectonic plates moving [as the waters rise].

'The second thing was to bring it up-to-date, to say to people: 'Look, you may think this is just a silly story, but you've been watching things like this on the news for the past ten years. These things have happened. There was that awful tsunami. It's not a million miles away from the world we live in today.'"

THE science element is an interesting one, because Jordan has noted how people often dismiss the Bible with a kind of knee-jerk reductionism - the notion that the universe can be explained by material interactions alone.

Jordan has no truck with this: "I don't buy into the whole Dawkins thing, that science has all the answers." It shows in the film. One way he modernises The Ark is by putting those materialist objections in the mouths of Noah's naysayers. "My brother-in-law is a scientist," a character says at one point. "He says the universe created itself, but man himself is God." "Well, in that case, have him make me one of these," Noah says, holding up a flower.

"It's not that I'm anti-science," Jordan explains. "It's just the pom-posity of saying definitively [that there is no God] when they can't even explain the universe we live in. I'm not trying to have a pop at anybody, I'm not trying to say to people, 'You should believe in God.' I'm just trying to explain that anybody who says there is no God, definitively, is a moron. And I genuinely believe that."

If this sort of thing makes him a target for atheist ire, he doesn't seem too bothered. If anything, he has became used to the idea of being regarded as a zealot. "I work in an industry where there are people who sold their souls a long time ago," he chuckles. "I've been in gatherings where people say: 'Didn't you do The Nativity? Aren't you doing Noah? What are you, some kind of religious nut?'

"You think, 'Er, no, not really. . . Where did that come from?' It's faintly ridiculous."

In fact, he has every intention of doing more Bible stories for mainstream TV. "If The Ark does well, then I'll go back to the BBC and say, 'Look, instead of doing this piece-meal, can I do a few films together? Five or six stories? A kind of mini-series?'"

Two characters he'd particularly like to tackle are Abraham and Samson; he thinks he could bring a fresh spin to them.

Ultimately, that's all he ever tries to do, he says. "I'm just fascinated by stories that everyone knows, but that I can tell in a different way. And the greatest source of those, I think, is the Bible."

Morocco may not be finished with him yet.

The Ark is on BBC1 at 8.30 p.m. on Monday.