Strictly speaking it would depend on it becoming a term of the contract by virtue of your purchasing decision, or your post-purchase decisions about the contract (e.g. which train you take on a flexible ticket), being influenced by the statement. See
section 50 of the Consumer Rights Act.
In practice that isn't a particularly high bar to satisfy in the context of a flexible train ticket. Note in particular that the above decision needs only be influenced ("[the statement] is taken into account"), not necessarily changed or entirely based upon the statememt. So I would suggest that the answer is yes, it's binding.