[10] CAF were selected by Arriva as they were the only manufacturer able to produce both new diesel (Class 195) and electric multiple units from the same platform, the Civity, thus increasing familiarity for drivers and reducing maintenance costs once in operation.

[6] Bombardier submitted a bid to produce electric units based on their new Aventra platform, but was unable to offer the matching DMU that Arriva required.

[13] Testing began in the UK in September 2018,[12][14] and in March 2019, a four-car Class 331 unit (331111) became the first train to be completed at CAF's Llanwern factory.

[16] During the first episode of the seventh series of Great Continental Railway Journeys, first shown in 2020, Michael Portillo drove unit 331005 inside the CAF factory in Zaragoza.

All trains fitted with an automated audio information system, as well as display screens – six in each carriage ensuring all passengers have an unobstructed view to at least one.

[18] Northern selected a "wide and spacious" vestibule area to allow for quicker passenger flows when boarding and disembarking to minimise dwell times which can result in delays.

As a result, they are fitted with Automatic Selective Door Operation (ASDO) for use on routes where station platform lengths are not sufficient to fully accommodate the train.