Surely what they have done is really quite a serious error.
A solicitor would probably agree; an uninterested third party probably wouldn't.
I guess it depends on perspective. If they dug up a prize flowerbed, or blocked access, then perhaps it is indeed serious.
If they made a genuine mistake, and only affected turf located outside a garden hedge that is easily re-instated, then it probably isn't serious.
If you want it moved, and they can't find a nearby alternative, then it is probably serious.
If you don't really mind, and are willing to negotiate a retrospective wayleave, then it probably isn't serious.
In the circumstances, however, you are within your rights to get them to remove the cabinet, and re-instate the ground to its former glory, at their expense.
Yes, we are concerned that a complaint may be detrimental to our village.
A complaint alone isn't detrimental. Insisting on removal, especially if they can't locate an alternative spot, while refusing to be open to negotiate a wayleave, would be detrimental.
Even if there is an alternative site that can be used, the cost of putting power into that site might make it economically non-viable again ... leaving the only option to remove the cabinet entirely.
Do people have service yet? Or has this cabinet only just been placed into position?
Not quite sure how they made the error, common sense would easily determine it as our property.
Please explain the context. It might be that your "common sense" answer isn't the same as other locations.
Also, the error could well have been made in an office (BT or subcontractor), mis-labelling the site as having a wayleave approved, or in the council or land registry, mis-labelling the site as public-owned.
Once tasked with the job, the blokes who do the actual installation work don't care about where they've been told to put it; they'll assume all the proper planning and approval work has already been done.