Saw some private contractors working in the front garden this morning. Leak seems to have been stopped for now. Japanese knotweed is a perennial problem with that property. I wouldn't be surprised if the noxious stuff fractured the water pipe. I've lost count of the times those garden walls been damaged and had to be rebuilt because of JK growing through them. On an unrelated point, the garden wall of a property across the road's also fallen over because of knotweed damage.