Illicit cannabis factory farmers are arming themselves with sawn-off shotguns, CS sprays and machetes and even setting booby traps to protect their crops from rival gangs, according to a police study published today. The report for the Association of Chief Police Officers (Acpo) reveals there has been a boom in cannabis production across Britain in the last two years, with nearly 7,000 illegal farms and factories uncovered in 2009/10 alone.