On weekdays you will get hourly HSTs each way, plus a number of stone trains to and from the Somerset quarries to London, hauled mostly by 59s and 66s with the odd 60 making an appearance. If you get up early enough there is also a GBRf departmental service.
Saturdays has roughly the same passenger traffic of HSTs, Sundays similar but with even less passenger traffic. No booked freight on either day. There might be a few railtours on Saturday morning with 47s and 67s, check RTI.