[2] The Sigma was created as a zero-emission single deck vehicle, marketed as improving "demand for cleaner solutions to public transport".

[1] The first Sigma 7 went to the Holkham Estate's Pinewoods Holiday Parks in Wells-next-the-Sea, for a bus service to replace the former Wells Harbour Railway,[8][9] while the first Sigma 12s were ordered by Whippet Coaches for delivery in July 2023, where nine will be used on the company's Universal network serving the University of Cambridge.

[12][13] On the Channel Islands, LibertyBus of Jersey took delivery of a pair of Mellor Sigmas in November 2023, which entered service the following month.

[14][15] The first Sigma for mainland Europe were ordered by Swedish operator Nobina for Gothenburg contract city services on behalf of the Västtrafic regional transport authority, with seven Sigma 7s destined for operation on Nobina's route T22 in the city's Angered and Bergsjön districts.

[16] 42 more Sigma 7s were ordered for Gothenburg demand-responsive transport services operated by Connect Bus in February 2023,[17] and three Sigma 7s were delivered to the German city of Kiel's municipal bus operator Kieler Verkehrsgesellschaft [de] in August 2023.