This paper describes the construction of a multi-level underground car park within a diaphragm wall in London Clay by the top down technique. The techniques used for diaphragm wall and pile construction under bentonite from existing ground level are reported. Column installation is described, followed by the excavation procedures and the method of construction of the sub-structure floors. Pin piling and casting of the lowest basement slabs completed the construction. An outline of the diaphragm wall and ground movements is presented. The as-built programme is presented and conclusions drawn. (A)