Class 319/3 units are formed in the following formation:
DTSO(A)+MSO+TSOL+DTSO(B)
Class 319/3 were converted from Class 319/1s by Thameslink in 1997-1999 for their Luton toSutton loop services, known as the Thameslink City Metro. Conversion involved removal of the First Class compartment in the DTSO end and repainting into Thameslink livery.
Upon First Capital Connect winning the Thamelink franchise, in 2006, their 'urban lights' colour scheme was applied progressively until completion in 2010.
In 2014, Govia won the Thameslink franchise and have started to remove the First capital connect livery scheme and replace it with their scheme of white with blue doors.
In 2015, Arriva Northern recieved 20 Class 319/3s for operating it's recently electrified lines. These 319s had there third rail equipment removed as well as recieving an interior refurbishment.