The Twentieth Century Society explain on their website that the idea of extending the original Old Bailey building was first proposed in 1960.  It was in reaction to this that McMorran's first plan for the extension was created.  However, when more land adjacent to the old building became available, the plans were revised, 

"... McMorran laboured over these designs, repeatedly and rhetorically asking ‘Am I doing the right thing?’. It was while he was working at home, however, that his eldest son, Alexander McMorran, who later qualified as an architect, suggested he might look to the work of Louis Kahn (1901–74) for inspiration." The resulting front "... is McMorran’s response: a highly original composition sculpted in stone and demonstrative of the compressive architecture he championed. It was, as one critic wrote some years later, ‘well ahead of its time in the abandonment of Modernist conventions, not for the new vernacular, but for a far more coherent and radical style’. (Brian Appleyard, ‘From God’s House to Bauhaus and Back Again’, The Times, 20–26 November 1982."