Darlington bought a batch of four Leopards which were unique in having a dual-door version of the Duple Dominant bus body.
The 3 service was a circular which mixed parts of the former 4 and 5 trolleybus routes, forming a radial link from the old Coniscliffe Road terminus through Mowden to Cockerton where it returned via Willow Road on the former 5 route which was the main haunt of the BUT double-deckers in their brief time in the town.
