A new BBC film follows the adventures of a pride of lions who - thanks to techno-wizardry, the voices of a starry cast and the skills of Men Behaving Badly writer Simon Nye - have been given the power of speech

Almost four years ago, I was asked by the BBC’s Head of Quirky Projects to attach some amusing dialogue to some wildlife footage of lions. I said yes, because that’s the kind of writer I am, and because there’s a small part of everyone over the age of 40 that will be forever Johnny Morris. Pride, that simple project about lions, has since mushroomed into an expensive BBC film. So expensive, indeed, that it has had to be reassigned to the BBC’s Worryingly Expensive Projects division. It will be shown over Christmas on BBC1, having blazed a trail from the US to Germany and France, notoriously hard TV markets to crack but obviously not averse to films featuring talking lions.

Pride: the film uses computer animation to bring movement and expression to the faces of wild or semi-trained lions

Working with the director John Downer, producer Christopher Hall and the hugely talented development team at Quirky, I came up with a story designed to make sense in natural history terms but that would still be entertaining, conceivably, to a six-year-old with attention deficit issues.

The cartoon The Lion King casts a long shadow over anyone writing a lion movie. Disney had several advantages: their lions could do anything because they were drawn, and any resemblance to the natural world was discarded when they had the lion-hero Simba befriend a warthog and whatever the other creature was. That just doesn’t happen out there in the African savannah, I discovered, having read the big book about lions that John gave me.

Problems emerged early on. In the wild, lions do a limited number of things. They kill other animals and eat them. And they have sex. That’s sort of it. So they engage in precisely the two activities you’re not allowed to show in a family film. They don’t do any of the staples of the genre, like hanging out at Edwardian railway stations or going to wizard school.

I did write a mating scene that I regarded as tasteful, arguing that it had scientific value. (Lions mate prodigiously, for days on end, then nothing for months. So very much like being a young single bloke living at home.) They argued that with sultry Kate Winslet and testosterone-heavy Sean Bean doing the voices, it crossed the fine line into filth.

Then I discovered that lions are, helpfully, very community-minded. They sit around doing very little for hours on end. Males are happier in the company of other males. Females are suspicious of or openly hostile to males. More contentiously, the female lions do almost all the hunting and killing, then the males wander up, push them out of the way, and eat it. I’m saying nothing. But it works for them.

There is a downside for males, though - they are all expected to leave home for ever and battle to take over another pride. So you get all your meals but you will have to fight to the death on a regular basis.

We duly fashioned an adventure story about growing up, rebellion, loyalty, bravery, and the problems of trying to be a vegetarian in a meat-eating society, and the director went off to Africa and filmed the lions.

The director John Downer is a natural history specialist. While the rest of us in TV have been sipping Styrofoam coffee in comfy rehearsal rooms as we explore the text, he has been waist-deep in swamp shouting "action", or more likely "jump, you bastards" at monkeys. He spends months looking down a lens at, say, bees. He has also pioneered the "bouldercam", a camera hidden inside a movable rock that acts as a spying device. (I’m looking to install a "pouffecam" in my own home for the same purpose.) Many of the amazingly intimate shots in Pride were captured that way.

Mouth to mouth: (clockwise from top left) Robbie Coltrane, John Hurt, Sean Bean, Rupert Graves, Helen Mirren, and Kate Winslet

Using a mixture of footage shot in the wild and of semi-trained lions, John filmed them doing everything the 90-minute script required. Nearly being stamped on by elephants. Swimming (they hate swimming). Being urinated on by cheeky baboons. He was gone for eight years. Well, two years, in fact, on and off. Filming wasn’t without its problems. The mongooses went on strike over the size of their trailers. A hyena stormed out of make-up, grumbling that her motivation was "tenuous". Or the equivalent.

But the hard work had only just begun. Pride is full of technical wizardry. You will believe lions can talk, even without the hallucinatory powers of a pint of Yuletide Baileys. Hensons, the company famous for the Muppets and doing things with pigs in Babe, were hired to animate the lions’ faces. The work is frighteningly time-consuming. Whiskers on the lions’ faces have to be added individually by computer. If I’d done it, they would have had two whiskers, one on each side, but these are professionals.

They had to redesign the lions’ jaws so that speech looked convincing. The software is improving all the time. When I wrote the first draft of the script, I was warned off suggesting that the lions smile or frown. They could talk, or not talk. Now they can make lions emote and gurn like Jim Carrey. Not that you’d want that.

The BBC made the always excellent decision to get themselves a sugar daddy: American cable channel A&E. I imagined that the price we would pay for this co-production would be them insisting on the cast of Buffy the Vampire Slayer (not that it’s not a tremendous show) playing the lions, but we were spared. The beauty of a large budget is that you get gorgeously expensive performers. And actors, even starry ones, welcome an acting job that you can do in an old T-shirt with a big spot on your nose. John Hurt, Martin Freeman, Helen Mirren. I could go on. Robbie Coltrane and Jim Broadbent, as two grizzled old lions. On Channel Five they would all have been played by two terribly keen students from RADA who can "do voices". (Not that they don’t do some excellent work on that channel.)

So do watch Pride when it comes round. It’s not every day you see real lions talking.

’Pride’ will be shown on BBC1 on Dec 27.