If you type in the date of 10/12 on www.fgw.co.uk only (doesn't work on NRE at the moment), you can find the December timetable for First Great Western services. I'm not sure if it's a work in progress at the moment, there are a few strange gaps on Severn Beach line services, including a train that goes back that doesn't go out (could be ECS or a 4-car train) and a 1 minute turnaround.