Train service codes (TSCs) are 8-digit codes used to relate train services to service groups for performance monitoring.
For passenger trains, this is '1' or '2' For freight trains, this is '5' or '7' For Eurostar services, this is '8'
Originally used as a geographic area code, but is now allocated without a pattern
3rd - 6th digits
For freight trains, this is the service group number. Its use for passenger trains is unknown.
7th - 8th digits
For freight trains, an optional sequence number for different origins.