It's not just the UK and all due to the price of meat. Saturday and Friday nights are prime times for the illegal meat shooters out shooting sambar. Not much gear is needed...rifle, thermal, a 4x4 tray back and a monster car fridge on the back. Wild venison taken this way will be cheaper than the beef in the shops but still give a good return to the poachers.
I can understand cash poor people buying this illegal meat but not the poachers. They're breaking a bucket load of rules.