On 14 February 1985, the BR board approved the substitution of the Class 91 for Class 89 for the ECML programme. The tendering process was relatively complex, but a decisive move appeared to have been GEC's offer of a sub-contracting arrangement to BREL for the construction of the locomotive's mechanical elements. It would be GEC's submission that would be selected as the winner; after which a contract for the construction of 31 Class 91 locomotives, along with an option for 25 more for the WCML, was awarded during February 1986. Shortly thereafter, BREL established a production line for the type at its Crewe Works.