How is it getting in, ie under/over fence/wall, under a hedge,self seeding, etc?

Its growing up their fence and grows through, under and over. I keep tucking it back over but it's just so invasive. I have to climb behind my hedges to remove it. The neighbours are wild gardners and don't seem to care or refuse to do anything with it.

The only solution I can think of is the last thing you want to hear. Go talk to your neighbor & explain the situation with much tact & diplomacy. Chances are they aren't even aware of the problem. That might be all that's necessary. Let them decide how to resolve it.

Thank you Bathgate but unfortunately we have tried this. They are also growing about 15 ash trees along the boundary of my front garden. We have clay issues and subsidence but still they insist on nature taking its course. Apparently they are very private people and like to be enclosed so another neighbour told me. :(

I have just added a photo of the front hedge which was taken two years ago. Now the tree hedge is enormous and cutting out my light........ What can I do?

I have ivy which grows up the stems of the old Leylandii trees which were let go, had to be hacked back and of course don't grow again. So it was bare stalks or climbers. The birds, bees and insects love the ivy - but it does like to creep where you don't want it. I chuckled when you wrote you tucked it back over! You can't be kind to ivy, it takes advantage! Hack it off the fence your side as much as you can (it will grow again), along the base of the fence I go along with a spade and cut through all the stalks back to the base of my hedge, then yank up all the trailing bits. It's a never ending job, but you just have to think of it as general weeding. As for cutting out your light with their trees, that type of issue is a minefield and might need a trip to Citizens Advice (if you can find one) and also mention the subsidence issue.
See here:
https://www.whnsolicitors.co.uk/newsroom/news/neighbours-tree-blocking-sunlight-garden-can-chop/

Or here:
https://www.inbrief.co.uk/neighbour-disputes/trees-blocking-light/
Nightmare neighbours, best of luck.

I have to agree 'a minefield'. It's a powder cake ready to go off. Seems like you can benefit from legal counsel. Find out if your rights are being infringed upon - get it in black & white for presentation in Court. There you go. Obtain a court order to have your rights enforced by decree by the Court - That's why it exists. (I'm in the US so my legal jargon may be off).

That's the path I would advise after all other attempts failed. Have your rights enforced by legal decree. If your neighbor fails to comply, he/she will be held in contempt of court which is a sticky mess for them - and expensive.

Thank you Honeysuckle and Bathgate. Your information is very helpful.

I saw an advertisement yesterday for a treatment that is claimed to kill ivy! It was called Doff ivy and brushwood killer. Might be worth investigating - and if it kills it on the neighbours side too they may not care.
Are you sure the fence is theirs? If it was yours that would give you more of a lever than if its theirs. As a general rule when a fence belongs to you the support posts are on your side of it, but no idea if this is infallible....

There are regulations about how high hedges between neighbours can be so if the ash trees are close enough to count as a hedge you might be able to get them on that. I think these regs vary with different councils so it might be worth enquiring locally what yours are.

you are right steragram re fences, the support posts should be on the owners side, but not a lot of people know that...me included ..so our small fence was erected with the support posts on the other side, for which I've regretted ever since, as the posts can be used for adding nails screws etc to support a training wire for climbing plants, which is more difficult on the 'smooth' side!!!

Oh dear that's very frustrating....perhaps you could nail through the panels into the supports if you used really long nails?

If the neighbours were to discover the rules they might think of laying claim to the fence - lets hope they remain in ignorance...