He drew this to our attention and has offered to move the one offending fence post, which he inadvertently set (in concrete) slightly out of line, a few inches into our garden. The rest of the posts are in line, on the boundary.
We like him, and have said it does not matter. But is that OK?
Leave it. The hassle of removing a concrete block is quite great and would leave a big muddy hole in your garden. Just make sure he doesn't make a habit of it every few months - you'll wake up one day and have an inch of garden left...
I would get him to confirm in writing that he has placed the post in the wrong place and that he will be willing to move it should it prove necessary. That way, if you want to sell, your purchasers have peace of mind over it, and, if he sells, his purchaser will know that the post will have to be moved at their expense.
Not worth getting him to do it now if you all get along, just worth getting everything in writing in case things change in the future.
if it's left there for a certain length of time then the land will become his so be prepared to lose that land- if it doens't bother you then fair enough but if it does you need to do something about it
The land won't become his. That will only happen if he didn't ask for permission, which he has done (in a roundabout sort of way).
Do get an agreement in writing just for your peace of mind. If it is really bothering you, suggest that he moves it now (after all, he has offered to) to avoid any problems in the future if either of you wants to move.
Leave it. Oh, please leave it. Otherwise we'll be reading about you in the Daily Mail, and how you are both going to have to sell your homes and live in leaky caravans after spending your life savings on legal fees. <photo of you looking sour beside a fencepost>
An easement may be created "by prescription". This happens when someone carries out an act (that is capable of being an easement) repeatedly, openly and without the landowner's permission for a period of least twenty years.
I presume this is what your solicitor and surveyor are talking about. The OP's neighbour has asked for their permission (by admitting what he's done and asking if they want him to move), so it is doubtful that he could later claim an easement. However, it is important to record the agreement (permission) in writing to avoid this.
The neighbour on the other side of them had lived there for years and they were quite good friends. When my neighbours needed to replace their fence, they decided, being good neighbours, that they would bring their fence a good few inches onto their own land to avoid asking their neighbour to cut down a tree which had grown right on the border. This was fine until the neighbour died and new neighbours appeared.
My neighbours needed to replace their fence again. In the meantime their neighbours had removed the tree so they positioned their new fence in a direct line along the border. The new neighbour demanded they move it claiming that any land he had weeded belonged to him! Being nice people, my neighbours did as he asked but are now stuck with the situation unless he moves and they replace the fence before any new neighbours move in.
Blimey, thanks, everyone. Too tired to take it all in atm, but will digest tomorrow. Most probable course of action will be to ask for a letter; and we're kind of hoping/thinking he'll move the post anyway rather than bother with writing the letter. (Altho of course that's a bit lily-livered: if we want it moved, we should just say so.) Aloha, thanks for your comments: we are v friendly (atm!) so can ask for the letter without causing upset. He has previously demolished part of our front fence by accident...and we didn't accept any money for that...
Have just had a chat over the offending fence, and rather than write us a letter, he is going to move the post. I thought that might be the result of asking for the letter, so I'm v pleased with the result.
Thanks yet again to the power of Mumsnet. All your advice v much appreciated.