More than six million Romany Gypsies live in Europe and many thousands of them have moved to Britain in recent years. The majority of new arrivals adapt to a British way of life, but some still follow a conservative Gypsy code called Pachiv. For those who live by Pachiv traditions, it is customary to marry soon after the onset of puberty. This practice breaks the law in the UK, where marriage is not legal until the age of 16 – which is also the legal age of sexual consent.

Earlier this year I spent two months filming with a Romany family for a Channel 4 documentary called The Gypsy Matchmaker, as the head of the family searched for a suitable teenage bride for his 14-year-old son Adrian.

Adrian is a bright boy who lives with his family in a modest Victorian terraced house in the outskirts of Oldham. The family left Hungary two years ago, moving to Britain in search of a better life. As recent arrivals, they see themselves as different from the more established Gypsy and Traveller communities who have lived in Britain for generations. While Adrian tidies his room, neatly folding and packing away his clothes, he explains his priority is not school – instead he wants to learn Gypsy traditions, passed down from his father in preparation for married life.

Adrian's father Sanko, 48, is a man who exudes total authority, with a voice like sandpaper and a disarming smile. Sanko already has nine children and 15 grandchildren and is determined to see Adrian, his youngest son, married as soon as possible. After a brief local search, Sanko identifies a 15-year-old Romany girl called Esme as a potential match.

On a windswept evening in late March, Sanko, Adrian and other members of their family travel to Esme's home, with a plan to formally propose the marriage to her family. Esme has no idea what is about to happen. She still goes to school and as far as contact with Adrian goes, she has had only one dance with him at a Gypsy Ball. Whilst some might see the beginnings of a teenage romance, for Adrian's parents, a marriage proposal is the logical next step. Adrian's mum tells me about Esme: "She is a young girl. We'll train her. We won't beat her. In a few years' time she'll be a patient wife."

As they drive west on the M60, Sanko discusses the merits of offering a cash deposit of up to £3,500 in order to secure Esme's hand in marriage. While these deposits are commonplace, there is no "standard fee" for a bride and weddings can also take place without money changing hands – but with other potential suitors circling Esme, Sanko wants to ensure he wins her for his son. An hour later, inside Esme's home, the potential teenage couple hardly speak a word as they exchange glances across the room. According to Pachiv custom, it is the heads of the families who negotiate terms. Romany Gypsy traditions are usually dominated by the patriarch, but the head of Esme's family is a woman called Banats – Esme's grandma – and it is she who will decide Esme's fate.

In the cramped back room the two extended families discuss the deal. It's standing room only. Religious icons hang on the wall overlooking two young mothers cradling their babies on the stairs. All eyes are on Sanko as he attempts to negotiate the deal and win his son a bride. Sanko starts by addressing Esme directly with the proposition, but she is too bewildered and shy to reply. Her grandmother, Banats, is less surprised. Like many traditional Romany Gypsies from eastern Europe, she herself was married at 14, and a few years ago, back in Hungary, she agreed to allow Esme's sister (who now also lives in Britain) to marry at the same age. But her new life in Britain has changed Banats, and she no longer approves of early marriage customs. She is not afraid to rebuff Sanko, and despite his hints of a cash deposit, she refuses the deal.

It turns out that this proposal is only the start of Adrian and Sanko's journey to find a suitable wife, and they invite me to witness Romany Gypsy gatherings in Oldham, Bradford and Bolton, eventually travelling back to Hungary, in order to find the right girl. It was in Hungary that I witnessed just how societal disapproval of Romany Gypsies can develop into full-blown hatred. The smartly dressed young woman I met, who moved into Adrian's old house in his home town of Pecs, brandished a loaded gun as she told me: "I think Roma children should be taken away from their family. A more radical method is to shoot them all."

Here in the UK, many traditional Romany Gypsy families are deeply concerned that the authorities will take their children from them if they are open about supporting early marriage. But when Romany families break the law and practice customs which are not only illegal but morally unacceptable in contemporary Britain, it is inevitable that they will fall into conflict with the authorities.

I believe my film captures traditional Romany family scenes with an intimacy not seen before on British television – let's hope it can open and inform the debate on how to approach this modern clash of cultures.