The design of the Class 156 was more conservative than Metro Cammell 's earlier Class 151 design , the bodyshell was made of steel instead of Aluminium , and the cab design was deliberately similar to the BREL Class 150 to ease union acceptance .
The design of the Class 156 was more conservative than Metro Cammell 's earlier Class 151 design . 
 The bodyshell was made of steel instead of aluminium , and the cab design was deliberately similar to the BREL Class 150 to ease union acceptance .