Can they really do this to us?

[Eatcabbage]

I bought my house 15 years ago and the current neighbours moved in about 10 years ago.
No physical boundaries have changed during or before this time that I can find record of, but now the neighbours say that the boundary is in the wrong place as it apparently doesn't match the Land Registry plan and I have to move it.
I've looked at the plan and it is very difficult to tell - their house has been extended since it was drawn, so it doesn't all match.
When the previous owners extended the house, the planning permission drawings show the fence in its current location.
Can they really force this fence move now? They have threatened to take me to court and make me pay their legal expenses if I don't do what they say.
It's not just a simple fence to move - it would involve moving trees, stone walls, oil tank etc. Basically half the garden would be pulled up.
I am a single parent, so am facing this alone and I have already had far more than my fair share of stress over the last few years.
I don't want my child to see our home pulled apart, but I don't want the stress of all this on me to have a negative impact on our life either.
I do have a solicitor, whom I am awaiting a response from. In the meantime I am losing a lot of sleep over this and I have had enough of waking up each morning feeling physically sick and like packing our bags and running away.
What would you advise?

I'd advise exactly as you've done which would be to use a solicitor. To me this doesn't sound like a small nudge of a boundary change but a significant loss of space to you. Dig in. Don't acknowledge them or any threats. Don't engage until you've had advice. Easy for me to say don't loose sleep, it sounds very stressful and I'm sorry you're going through this. 💐 Get on the phone and nag the solicitor daily. Also check your neighbour isn't beaching any old convenants .....that'd put the shitters up them. Get the solicitor to search that too.

Obviously your own solicitor is the only one who can properly advise once they've seen the title plans. Unless a proper surveyors plan has been prepared then they cannot know that the boundary is wrong, the thickness of the line on an office copy title is basically a metre wide so that gives a massive variation in real life. There should be no cross over of the boundaries on the filed plans so their boundary should match with yours. A decent Conveyancing solicitor should be able to look at the plans and give you an idea if you have anything to worry about. In the meantime it's worth looking at google maps aerial view alongside your title plan and see whether the physical boundaries look generally like they are in the same position as your plotted boundaries. Ignore how close their property is to the boundary if they have built an extension and look at surrounding properties/structures to give perspective. Sorry if that's not too clear, it's difficult to describe how to do this!

The LR plan is not determinative, and should only be used as a rough guide. What's far more important is how it looks on the ground. Make sure you claim under any household insurance legal cover.

I think if the fence has been in place for 10 years, you take the land via adverse possession.

A friend told me that if someone has been using something for 15 years, it legally becomes theirs. (This was relevant to her as a neighbour wanted to use her driveway, which my friend wasn’t using. She said the neighbour could use it but only if she signed something to recognise that the driveway belonged to my friend.) If what my friend said is right, then even if the extra land wasn’t yours in the first place, then it would be now that you’ve been using it for 15 years.

Can you find the records from when you purchased the house, as if wrong the solicitor who did the work when you bought might be liable.