A reporter, posing as a migrant wanting to cross, helped us gain unprecedented access to the smugglers' notorious forest hideout in northern France - an area plagued by armed battles between rival gangs. Secret filming at a major UK railway station also captured associates of the gang collecting cash payments to secure migrant places on illegal Channel crossings.

Two men met us on separate occasions on the busy concourse at Birmingham's New Street Station to collect envelopes containing hundreds of pounds. Multiple sources have described how gang leaders, who keep one step ahead of the authorities by changing mobile phone numbers and the gang's name, subjected their henchmen and migrants to violent beatings. We have managed to identify three men - Jabal, Aram and al-Millah - all Iraqi-Kurds, who are believed to lead the outfit, which is one of the main groups in northern France transporting people to the UK by small boat. We have also come across other senior figures, including a man called Abdullah, whom we witnessed shepherding groups of migrants towards boats. Another gang member, Besha, who had escorted migrants in France, took a small boat to the UK himself, we learned, ending up in a migrant hostel in West Yorkshire having claimed asylum. The findings are the culmination of months of undercover fieldwork and the creation of multiple fake identities to engage with the smugglers. We have been able to build a detailed picture of the gang's tentacle-like structure and the ways it has successfully evaded the police. (BBC)