Question
I have constructed a wooden plant pot approx 9" x 52" and attached it to the side of a breezeblock wall, filled the base of the pot with concrete and put soil/compost on top; I planted 3 tall conifers inside the pot and would like to know the likelihood of the conifers surviving, bearing in mind that I have filled the base with concrete and the narrowness of the pot - they are already starting to go very brown from the base upwards

Answer
Very little chance for a tree to grow in this situation--too little soil depth for the root system to grow and the roots will not be able to get enough moisture and/ or food to survive. I suggest that your plant something other then a tree in this confined space. Sorry!