The new documentary film Blood in the Mobile by Frank Piasecki Poulsen tracks just how much your mobile costs. Not to your wallet, but to the lives of people who mine the minerals that make up its parts.

The film, which focuses on Nokia, discovered children working for up to 72 hours at a time in narrow underground mines in Bisie, Congo.

The mineral coltan, or tantalum, which makes up the capacitors in mobiles, can also be mined in many other countries on the planet, including Australia, Canada and Brazil.

Ole Tornbjerg, the film's producer said: "It was very important for the director to film in the Bisie mine. So important that he actually risked his life to go there. For him all the warnings not to go there, made him even more persistant that he had to go there and document the digging of and trade with minerals which ends up in our cell phones."

Four days before the premiere of the film in 2010, Nokia promised in one of the biggest Danish newspapers to stop using conflict minerals. Some months later, Nokia withdrew its promise.

In an interview with BBC radio, Poulsen said that although he focused on Nokia as that was the maker of his handset, the issue of conflict minerals applies to all mobile phone makers, and by extension, all mobile phone users.

The film-makers encourage mobile phone owners to take action by filling out a form letter and sending it to their local MP.

Blood In The Mobile will screen in the UK from this week:
Friday 21 October - Thursday 27th October London – Empire West End
Wednesday 02 November London – Royal African Society
Monday 07 November London – Hackney Picturehouse
Thursday 17 November Bath – Bath Film Festival
Friday 02 December - Sunday 04 December Belfast – Queens Film Theatre