Robin Campillo’s new movie, Red Island, is an amazing, moving evocation of his own childhood in Madagascar as what the Anglo-Saxons call an “army brat”. His soldier dad was posted there with the family in the early days of the island’s independence from French imperial control – and the 10-year-old roamed free in this lush and gorgeous place, but all the time aware of sexual licence among the grownups, their wan melancholy at their imminent expulsion from this paradise and the increasingly pointed anti-colonial rumblings among the Indigenous people. The boy is almost like young Jim in JG Ballard’s Empire of the Sun (played by Christian Bale in Spielberg’s film version) wandering with absolute liberty in the chaos of wartime occupied Shanghai – only here it’s with more sunshine and more erotic languor.

When I meet Campillo in the London offices of his UK distributor Curzon, he is a dynamic, athletic and yet also somehow cherubic figure with close-cropped grey hair (you can almost see him as a little kid), sparkling with energy and eagerness to talk about this movie, along with his career and what it all adds up to so far.

He has long been a powerful presence in French and world cinema, both as editor and screenwriter for the works of director Laurent Cantet, including Time Out and his Cannes Palme d’Or-winning schoolroom drama The Class, but also as a director for his own movies. His cult neo-zombie film They Came Back was developed into a hit streaming series for French TV; his intense drama Eastern Boys was nominated for Césars and won an award in Venice.

And most prominently, his overwhelmingly passionate 120 BPM (Beats Per Minute) in 2017 – based on his own experiences as a gay man in 80s Paris, working for the activist group Act Up, demanding action on Aids – was the film that Pedro Almodóvar declared to be his favourite at Cannes and had Barry Jenkins raving on social media. Now he has surrendered to the flow of memory and reached back into his own past.

I tell him that Red Island and 120 BPM show that his great theme is freedom: its possibilities and responsibilities, pleasures and sadnesses. He gives qualified agreement. “When I was in Act Up and when I was in Madagascar, I was not thinking about these things as cinematic experiences. But when I recall Madagascar I can remember everything about it. My work as a director started at this point, but in an unconscious way. It took me 50 years to realise it.”

He says that he is fascinated by transition: the old world becoming the new world. In 120 BPM he showed the 1980s as a time when gay men were afraid of the new epidemic, but Act Up helped usher in a new era when they were determined not to be victims either of the illness or the silence surrounding it. In Red Island, it is about the placid French imperial entitlement of the 60s giving way to the new independence movement in the 70s.

His own childhood was made up of a complex Frenchness: “I was born in Morocco; I was born into a colonial situation. We were very French as a family, but we were afraid of the idea of living in France because of what it would show us – that we were poor. Not so in Morocco. When I was four years old, our family left Morocco and we were briefly in Metz in Lorraine, a sad, cold place where we realised how poor we were. But then we went to Algeria, where my dad was involved in the transport of France’s nuclear weapons and then we went to Madagascar. And it was like a dream.”

But he says it was a dream that was being confected on his behalf by adults who couldn’t tell him what was going on. “For me it was real happiness. But it was over-acted by the grownups, trying to convince me of happiness, putting on a fairytale show in front of me, like Sesame Street on TV. Behind the dream there was always military guys in camouflage.” Campillo draws on a maxim by Gilles Deleuze, about being “trapped in the dream of the other”. The Malagasy, the people of Madagascar, were themselves trapped in the French imperial dream.

The film shows the racism and hypocrisy of sex on the island. Soldiers were permitted and even tacitly encouraged to visit the local women at the brothel, but the idea of falling in love with one of them was horrifying. One of the film’s most amazing scenes shows a French officer of this sort submitting to an exorcism from a priest. All quite accurate, says Campillo, although he discovered it in later life, through his research for this film: “My parents talked about soldiers who fell under the local women’s ‘spell’. They would talk about magical philtres. But it was a racial thing, a phantasma.”

The whole system, he says, was infantilising: “Thomas is a minor (a child) in the story. The figure of Colette [corresponding to his mum] is a child compared to her husband Robert; Robert is a child in relation to his general and the Malagasy are children in the eyes of the French colonists.” In the film and in real life, the boy called Thomas (that is, Robin himself) had a friend called Suzanne (in real life, Nicole) a little girl his age that he went everywhere with. Leaving her when they were cast out of Madagascar was heartbreaking and the end of childhood.

So, given that his previous film was such a big hit at Cannes and this one is so good – wasn’t he upset that Red Island was not included at Cannes this year, an omission much gossiped about? Campillo laughs … and says he can never be sure what is in the mind of the festival’s legendary chief, Thierry Frémaux. “I sent Thierry a message saying that the movie needs to be in Cannes – the story of Madagascar is a forgotten page of French colonial history. Where else but in Cannes should the story be told? Thierry replied simply that he ‘had to make a choice’.” Campillo smiles good-naturedly, indicating that he understands the realities, and he applauds the Cannes successes of his friends Catherine Corsini and Justine Triet.

Now he is making a futurist movie inspired by his 17-year-old daughter, a speculative film about what she might be like at 90. But who to cast? He muses over Charlotte Rampling, Susan Sarandon and asks me what I think of Emma Thompson. A great idea. Emma Thompson as Campillo’s grownup daughter of the future sounds unmissable.

• Red Island is released in the UK on 1 March.