After having a look through last year's diagrams, they say that the 15:36 off Kings Cross is booked for a 321, the 16:32 a pair of 317s, the 16:54 (Cambridge service not Welwyn terminator) a 317, the 17:22 a pair of 321s, and the 17:52 a pair of 317s.
These are from last year's diagrams, but I...