To tell my neighbour he's a fucking knobhead

Shocking how many people think you should be going round and cutting the hedge. It was nice of you to do while you did it but as you've rightly researched, it's not your responsibility to.
As annoying as maintaining a hedge that you didn't ask for is, it's just one of those things in life / law.

For everyone saying it’s OP’s responsibility. I have an elderly neighbour. Her garden plants are invading my garden. We had to get a new fence as they had grown through. They are not my plants, I didn’t want them. Surely I should be making her keep them trimmed going off the consensus on here.

What HE needs to do, is cut the branches back on his side of the hedge and then put up a fence so the trees don’t affect him. And YOU need to keep them to less than 2m high (that’s under 7’ tall) and ensure that the trees don’t damage his fence.

But the neighbour has made it dangerous, if not impossible, for them to cut the hedge by piling unsafe rubble up against it!

Of course you should trim the hedge. We have a hedge that grows on the other side in our neighbours garden. It’s an absolute no brainer that it’s your responsibility. You are also out of order to call him what you did. He sounds like an idiot.

Seems very simple when you put it like that.

In that case you were daft to even start cutting them in the first place.

Leaving aside whose responsibility it is to cut the neighbour's side, in your shoes I would offer to do it just to avoid him doing something destructive himself. I wouldn't want to actually talk to him given his aggression, but would write (keep a copy) saying you want to cut his side but access is difficult on his side, so could he remove rubble, make an even surface etc. so you can do the work. Keep a record of correspondence and any incidents, plus when work is done to the hedge.

It's unusual for a hedge to be fully dogproof.

If the hedge were to become damaged, it would be his responsibility to keep his dog contained so he would need to put a fence up, even though (presumably) the boundary is yours. Your job is just to maintain the boundary, you have no obligation to make it dogproof. However in practice this would just be a different, nasty battle to have with him.

People who know the detail of the law are usually different people from those who threaten and demand things from their neighbours.

I'm still glad I live next to my neighbours, who cut their whole hedge, though.

You sound very selfish. You should be maintaining the hedge why should they need to do any work on something you want. Our neighbours have huge trees that overhang our boundary. I hate them and the work it takes us to maintain them. Constantly clearing up the leaves in the autumn and winter.

I think you’ve been very reasonable with his mum and although I can’t say I like anyone being called what you called him, you aren’t wrong! But I am genuinely worried you may have put yourself in danger - he sounds dreadful! Please document everything, call the Fire Brigade for any big/dangerous fires, and the Police if you feel threatened. I can’t imagine how scary all this is :(

It’s not really! You have no legal right to enter your neighbours property. You’re not even likely to know who they are if they’re at the back rather than next door

This summer, I got a gardener to cut some overgrown ivy at my back which could best be done from the other side. First I had to work out which street it was in, find exact house, ask the resident’s permission to enter her garden then warn her of the exact date and time that a strange man would be appearing in her garden!

If I bought a house that already had established hedges, there’d be no need to cut the neighbours side. OP has said they’re her hedges, implying she planted them, well then she has to take responsibility for them invading her neighbours. OP later said, they’re not something we’d have planted, so actually, no idea what’s going on as OP seems to change her mind. But, if they’re not OP’s then why say they are, and why cut the neighbours side for 20 years 🤷‍♀️🤔

He sounds awful but I'd really hate to be having to deal with the work and expense of trimming a hedge like that. They are ugly an a pain to keep tidy. If you got it cut right back on his side the. It won't regrow where it's been cut back to if it's cut back far enough. . That would be worth doing to stop the aggro.

He could potentially get you to reduce the height using the high hedge legislation. I'm not sure though.

That is not what the law says.

Couldn't have put it better myself. A pox on both your houses!

Me too. It’s so inconsiderate. Leyandis suck all moisture out of the surrounding soil too. They are such hideous things to live next to.

When it was just the older woman living there, OP's husband DID cut the hedge whenever she asked.

Then her younger son moved in, presumably fit and healthy as he's a builder, and made the ground on his side of the hedge unsafe for anyone to cut said hedge. Then comes round in the depths of winter (so already unsafe ground made even less safe by a covering of snow) and verbally abuses OP's daughter. No asking nicely as his mother used to do, just aggressively confrontational from the word go the first time he demanded that the hedge be trimmed.

I think the "common decency" bird oft quoted on this thread flew away at the first encounter.

It's not the law though. It is showing advice for councils and if you read the linked pdf file then it says that a tall hedge by itself is not valid for a complaint and should be dismissed. However if the tall hedge is right next to the complainants window then it should be followed up (loss of light). So it needs an extra factor with the over 2 meters for it to be valid.

We have 75m of hedge down both sides of our garden, but both are ours. They were here before all our neighbours, and before we moved in. There are no fences, everyone knew what they were getting when they moved in. Hedges grow, if they grow into your garden, you cut them. That’s how it works.

If you’re cutting 4 lengths of hedge (both sides x 2?) good luck to you.