Movie villain happier to be real-life hero

'There is no good side to celebrity," Javier Bardem laughs. The Spanish actor knows all about the price of superstardom. One half of Spain's most famous couple – Penélope Cruz gave birth to their son just over a year ago – he is as successful in English-language movies as those in his mother tongue. He won the Best Supporting Actor Oscar for his brutal turn in the Coen brothers' No Country for Old Men and was nominated in the Best Actor category for playing the gay Cuban writer and poet Reinaldo Arenas in Julian Schnabel's Before Night Falls and again in 2011 playing a criminal clairvoyant in Alejandro González Iñárritu's Biutiful. Bardem's claim about celebrity feels especially disingenuous as the 43-year-old actor was recently at the Berlin Film Festival as producer and presenter of Sons of the Clouds: The Last Colony, a documentary about the plight of the Sahrawi people in the former Spanish colony of Western Sahara. Using fame to highlight a political cause is a path well-trodden by actors.

Bardem is an impressive figure. He is very personable, flashing his devilish electric smile at all the right moments, and has the ability to make you want to agree with his every word. Yet there is also a sense of disappointment that for all his efforts to push the issue of the Sahrawi people into the public consciousness, including speaking at the United Nations, it will never garner as much media attention as his relationship with Cruz.

They married in 2010 at a private family ceremony in the Bahamas in an attempt to avoid press intrusion. Today, he deflects questions on his relationship, saying that it shifts attention away from his work. "It brings some other pressure and expectation that maybe the movie doesn't deserve," he says. "It can help in some ways, but not in others.. I guess these ideas belong to people's perceptions from the outside. But we're used to that. There are perceptions from the outside and then there is us. The real us."

It's tough to sympathise with someone whose life appears so glamorous. Yet the flipside of the glamour, he says, is balancing work with the impact it has on the rest of his life. "I do a job and am lucky enough to do a job that I love, but it is a hard one. I'm not saying it is as hard as working in a coal mine, but it is still difficult in a different way. Sometimes you have to go through very strong emotional journeys and then come back to yourself. And that can be difficult to control."

Sons of the Clouds begins with Bardem's visit to the FiSahara Film Festival in 2008, which takes place in Dakhla, a refugee camp in the Algerian desert. Invited guests stay with Sahrawi refugees, a stark contrast to the five-star hotels in which luminaries are usually housed at film festivals. It was getting to know his host family that led Bardem to his decision to raise awareness of their plight.

The Western Sahara was once a colony of Spain, so is this a collective colonial hangover? Bardem laughs: "I've never heard that term before." The film gives a potted history of the Sahrawi people, explaining how, when the Spanish left, Morocco claimed the desert as their own under protest of Algeria, where a resistance movement, the Polisario Front, is still based. French and US interests also add to the general confusion. The actor separates the sentiments felt by the Spanish populace from the stance of various Spanish governments on the dispute. "The population is really aware of it and supportive of the Sahrawi people. But no government has done much about it, because it is a hot potato... they will be forced to face Morocco in so many ways and they can't, or they don't want to," he says. "But the Sahrawis have a lot of support from the population in Spain. So, yes, there is a hangover, I guess, but it is really painful for the government."

Born in the Canary Islands, the youngest of a family of actors, Bardem learned English by listening to heavy metal, in particular AC/DC, and is known for speaking up on issues he believes in. An atheist, he created controversy after the legalisation of gay marriage in Spain when he said in 2005 that if he were gay, "I would get married tomorrow, just to mess with the church." Last year, he joined the Enough Project, an organisation that raises awareness about conflict materials in eastern Congo. In a YouTube video supporting the campaign, he starts by admitting that he's a mummy's boy, saying: "The older I get, the more you realise that my mother was always right."

As for the list of actors who put their names to political campaigns, he does not think it a surprising phenomenon. "Movies are powerful. But I think everything is political. When you put gas in your car you are making a kind of political statement. Of course there has to be a relationship between politics and film.

"The question is, how far do you want to go with it? If you feel you should do something, then do it. And do it in a way, or form, or shape that you think can help the best, which in my case is making movies."

The next year will be a big one for the actor, with roles in two hotly anticipated films. First up, the as-yet-untitled Terrence Malick picture rumoured to be heading to Cannes. "Of course I cannot tell you what it is, or what I do," says Bardem, maintaining the secrecy that surrounds Malick's films. What is known about the picture is that it stars Ben Affleck and Rachel McAdams, and is about an American man who reconnects with a woman from his past after his marriage to a European falls apart. Bardem plays a character called Father Quintana.

Then comes the fulfilment of a childhood dream. He will play the villain in Skyfall, the new James Bond film. "I was born watching James Bond movies and there are many reasons to do this – the cast, the script, the story, the role and, of course, [director] Sam Mendes," he says.