Broken paving slab is causing water ingress and damage to masonary

A paving slab between 43A Gloucester Square W2 & 4 Southwick Place W2 is broken in several places and I believe it to be the cause of terrible water ingress to the masonry at basement level of 43a Gloucester Square. (see photos). I have checked the basement of 4 Southwick Place and no water escape there. The exterior stucco of my home was completely renovated within the last year and look how quickly the damage has returned. A surveyor has looked and believes the broken paving slab is allowing the water to seep in. The walls are now completely sodden. Please can you arrange to have this paving slab replaced and made water tight. Thanks