Chris

Fair enough, but the question isn’t likely to be whether or not you own the land - if the box visibly interrupts the natural line of the boundary wall, you almost certainly do own it. The point is, did a previous owner of your house grant permission for the box to be there? If they did - and they almost certainly did - then it is going to be very difficult and very expensive to get the box moved.

If the wayleave exists, then when you bought your house your solicitor should have drawn your attention to it during the usual search process prior to purchase. If you kept all your correspondence from that time, you might find it, which would save you the cost of having the search done again.