The Enviro400 MMC is available powered by either Euro VI diesel, compressed natural gas (CNG), hybrid-electric or fully-electric powertrains.

The Enviro400 MMC can trace its design roots back to 1997, with the introduction of the Dennis Trident 2, one of the first low-floor double-decker buses to enter service.

The model saw immense success at the turn of the millennium, despite financial difficulties facing Dennis Specialist Vehicles during this period.

Compared to the Enviro400, changes included a complete body redesign with new front and rear ends and Euro VI engines as standard.

[16][17][18][7] National Express West Midlands (NXWM) also operate a large number of Enviro400 MMCs, mainly for its high-specification Platinum network.

Built to Transdev's own "Sky Class" specification, fourteen were allocated to the Witchway X43 between Burnley and Manchester, with next stop announcements on these buses voiced by Coronation Street actress Jennie McAlpine.

[53] The remaining five of the new vehicles were allocated to the CityZap express route between Leeds and York, featuring next stop announcements voiced by BBC Yorkshire and Lincolnshire weather forecaster Paul Hudson.

[67][68][69] The first production examples, built with hybrid powertrains, entered service with Arriva London on route 78; a repeat order in 2016 would later see this fleet grow to a total of 53 Enviro400 Cities.

The Enviro400 XLB features essentially the same body style as the standard Enviro400 MMC, but stretched over three axles and fitted onto Volvo B8L chassis.

Lothian Buses were the launch customer for the Enviro400 XLB, with an initial order of 42 vehicles for inner city core routes,[71][72] which was followed by further examples delivered later in the year for service on the Airlink network to Edinburgh Airport.

The only other operator to take delivery of Enviro400 XLBs was Stagecoach East, who took twelve equipped with guide wheels for use on the Cambridgeshire Busway in early 2020.

[73][74][75] The Enviro400H hybrid electric platform developed by Alexander Dennis and BAE Systems was carried over from the previous Enviro400, and the first examples of the type began to enter service in 2015.

These are geofenced to operate in electric mode when entering Brighton city centre's Ultra Low Emissions Zone (ULEZ).

[90][91] Seven Scania N250UDs with Enviro400 MMC bodies were introduced to First Essex in 2020 to upgrade Airlink services connecting both Southend and Stansted airports to double-deck operation.

The first 13 Enviro400 MMCs bodied on the Volvo B5LH hybrid chassis were delivered to Stagecoach Strathtay in 2015, who uniquely employed conductors aboard the buses allocated to the 'Tayway 73' service - which runs from Arbroath to Ninewells Hospital.