So we are fairly sure what it is, the question remains, how it got there, especially in its present state.
If it was the remains of a practice round, I would imagine that no warhead would be present therefore no detonation would take place, therefore the propulsion section would remain intact.
The location is only 15miles from Otterburn.
Does it look like like a practice round. Could it have fallen from its mount at some point in the past ?