It depends on whether the job grade has had a pay and conditions 'restructuring' since British Rail days.
For Drivers on GTR restructuring did take place and they don't get any enhancements for unsocial hours etc.
Back in BR days there was a 'Variable Roster Payment', an 'Irregular and Unsocial hours Payment' a 'Driver Only Operation' payment, as well as enhancements to hourly pay for Saturdays, and for hours between 21:00 and 06:00.
As I said, for drivers that's all gone now and incorporated into basic salary.
If you tell us what grade you are looking at there might be someone who can help.