Parcel logistics in urban areas are characterized by many carriers undertaking similar activity patterns at the same times of day. Using substantial carrier manifest datasets, this paper demonstrates advantages from rival carriers collaborating using a “carrier’s carrier” operating model for their last-mile parcel logistics operations. Under these circumstances, a single carrier undertakes all the deliveries within a defined area on behalf of the carriers instead of them working independently. Modelling the daily delivery activity of five parcel carriers working over a 3.7 km2 area of central London, comprising around 3000 items being delivered to around 900 delivery locations, and consolidating their activity through a single carrier suggested that time, distance and associated vehicle emissions savings of around 60% could be achieved over the current business-as-usual operation. This equated to a reduction in the number of delivery vans and drivers needed from 33 to 13, with annual savings of 39,425 h, 176,324 km driven, 52,721 kg CO2 and 56.4 kg NOx. Reliance on vans and associated vehicle emissions could be reduced further by using cargo cycles alongside vans for the last-mile delivery, with estimated annual emissions savings increasing to 72,572 kg CO2 and 77.7 kg NOx. The results indicated that consolidation of items for delivery in this way would be especially beneficial to business-to-consumer (B2C) carriers whose parcel profiles comprise relatively small and light items. One of the key barriers to the wider take up of such services by individual carriers is the loss of individual brand identity that can result from operating through a carrier’s carrier.