Does it need moving to a safer location?
There is not a simple answer to this question, apart from saying don’t do it if you can avoid it.
Milestones should stay in their original position, unless the original position disappears or becomes too dangerous for the survival of the milestone.
Moving a milestone further back from the road edge is the best option, since this maintains the correct distance along the road from neighbouring milestones and from destinations recorded on the milestone.
If the milestone is in a sequence, they will usually be all on the same side of the road. This means it may be better to move the milestone a few metres along the verge on the original side, rather than across the road.
If the milestone is listed, the listing will fix the position, and only under very exceptional conditions can a listed milestone be moved, although this has been done in the past.