It is a telegraph pole... which Wikipedia says holds the record for the UK's smallest telegraph pole - maybe the world's.
The pole was placed there in the 1860s as part of a string of telegraph wires and poles along the Shropshire Union Canal, and this is the only one of them to survive. Without its wires nowadays...
If you want to glimpse it yourself, you'll need to get on the canal near the village of Woodseaves and head for 'High Bridge'.
By the way, this part of the canal is in a deep cleft, which is why the bridge is so high, supporting the road that passes over it from ridge to ridge. The bolstering extra arch - on which the pole is placed - had to be inserted because the strain on the walls was so great.