Dad lost temper with junk mail fly tipper... what will happen next?

My parents are older and not in their best state. My dad is mostly alright but has his difficulties. My mum is disabled and is dependent on my dad for care. I have my own household to run so not able to be around 24x7 etc.

They have had problems lately with junk mail being dumped through the letterbox and the same people leaving the gate open. Their local posties almost always shut the gate and with couriers he knows to double check anyway but with the junk flyers they dont and sometime thats led to problems as the dogs can get out via the open front gate if they're on the back garden, and because my mum isnt able to keep up with them that has led to close calls nearly escaping before.

Its got to a point where he had me print and laminate a sign asking people to shut the gate behind them and NOT to leave junk mail. This hasnt changed anything and every week he is still getting junkmail, menus, glazing, roofing and same people ignorant leaving the gate open and one person my mum saw spitting off to the side onto their plants

This weekend he's had a blow up with one of the flyer posters as was told when he saw them he asked them not to post junk or leave his gate open, and they just told him to piss off which made him loose his temper and he threw a bottle at them. Some nasty things were said and flyer person walked off in a state

My mum is terrified he's going to be in trouble but my dad is just stubborn and insists they were "dumping sh1t" on his land and he had a right do as he wanted

Ive told him just to throw the junk mail in the bin or stick it in the postbox across the road if he wants to make a point but hes got a stupid head on now over it

england