These two fleets of Class 319s were introduced to power the Thameslink services introduced from the late 1980s providing a south-north cross London service. The 46 Class 319/0s emerged in 1987, followed by 26 slightly revised sets in 1990. The units were fitted with dual power collection (750V dc third rail and 25kV ac overhead) and were allocated to Selhurst depot in south London.
With the changes in the rail network leading up to and after privatisation, the operation of these sets slightly altered. The first 13 sets of the Class 319/0 fleet were allocated to South Central and used for domestic outer suburban services working of the dc system only, many sets lost their 25kV ac equipment. A further seven sets were heavily rebuilt by Railcare Wolverton and classified as 319/2, these are dedicated to the express Victoria-Brighton 'Brighton express' service with low-density interiors.
The sets allocated to Thameslink under privatisation, the 26 Class 319/1s and 40 of the original Class 319/0s were all given major refurbishment. The 319/1s became 319/3s and are dedicated to the Thameslink 'Metro' services, while the Class 319/0s were rebuilt with first class accommodation in one driving car and allocated to the Thameslink 'City Flier' express services. When delivered the 319s were painted in NSE colours, this is retained by the South Central sets. Units operated by Thameslink are now in the company house colours.