After some contact with Openreach one of the very helpful team arranged to bring it up with one of the local high ups and he arranged to get a visit from a couple of engineers. All done from the property side after a visit. Basically up the ladder and noticed the clamp wasn't clamped tight and the cable appeared to be pulling from the wall and through the unclamped clamp.
The chap took out some cleats, pulled cable through some more and then fastened the clamp up. He said if that fails then a new clamp next.
Will keep an eye on it, especially when the wind picks up. There is still some slack but not to the extent of before where it drooped a lot.
Will monitor.