NOTES: This steel-framed building was designed on two floors around a central courtyard according to American out-of-town planning principles by the Chicago firm of Skidmore Owings & Merrill (SOM) in association with the London firm of Yorke Rosenberg Mardall. This extremely influential building with its use of high-class welded steel and the open-plan design led the way for the subsequent development of 'high-tech' steel office buildings for which Britain became internationally renowned. It was Grade II listed in 1996.