Multiple working

Early diesels were also fitted with communicating doors in the nose which allowed the secondman to access the train heating boiler of the rearmost locomotive.

For this reason, the drive selector on the Class 127 was fitted with positions marked "D, 3, 2, 1" to change the gears when working in formation with vehicles with mechanical transmission.

[5] First-generation DMU coupling codes: Most second-generation units built by British Rail were designed to use the BSI multiple working system, including members of the 14x Pacer and 15x Sprinter families.

Some post-privatisation trains such as the Class 168, 170 and 172s[6] were fitted with BSI couplers enabling them to operate in multiple with older stock, while other incompatible systems emerged.

[9] Franchise changes and stock reallocation means that many train operating companies use fleets with a number of incompatible multiple working systems.