My question really is can I put back the fence which was the boundary line between the properties.
The legal boundary hasn't move just because they've put a new wall in place.
Exactly. As others have said, you can do what you like within your own boundary, as long as you comply with any local restrictions on fence height etc. As your neighbours are moving, this is a rare opportunity to do something without potentially upsetting anyone.
A trowel in the hand is worth a thousand lost under a bush.
If the deeds show that the fence was your responsibility then they should not have taken it down without your permission. They should put it back. If their wall is on their land inside the old fence boundary then I would have thought you could put the fence back if you don't want to persuade them to.
Dordogne and Norfolk. Clay in Dordogne, sandy in Norfolk.
They took it down with permission from the previous owners, BL: "our next door neighbours persuaded the previous owner to let them take
down her 1.8mtr fence and build a brick wall on their own property"
A trowel in the hand is worth a thousand lost under a bush.
Unless there's anything in your deeds or local bylaws that says otherwise (and assuming we're not talking about listed buildings) you can put up a fence on your own land. And as @Hostafan1 says, the boundary hasn't moved (and if it had you'd have gained some land!). Just make sure you know where the boundary ("a line of no width") is.
There's some information on permitted fence heights here. You can probably go to 2m if the extra helps privacy-wise.
I know of a case where somebody errected a fence on their side of a tree
which belonged to them - to all intents it looked as if the neighbours
owned the tree, but they didn't. Never did find out what was going on
there.
Pat, there is nothing to stop you from erecting a fence on your land in front of their wall, which was presumably already there when you bought the house. Whether you need to put a 1.8 metre high fence if their garden is lower than yours is for you to decide but if it would then cast a lot of shade on their side then the new owners may be able to get you to lower it. You might be better off with a lower fence, with perhaps some lovely shrubs in strategic places or as Stuart says a trellis on top.
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There's some information on permitted fence heights here. You can probably go to 2m if the extra helps privacy-wise.
I know of a case where somebody errected a fence on their side of a tree which belonged to them - to all intents it looked as if the neighbours owned the tree, but they didn't. Never did find out what was going on there.