If it's a big fast one then you need to book but if it's not then normally you can walk on. Get to the station a little early and try and get reservations for both, if you don't need them they won't give them to you.
@snottyotter started
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If it's a big fast one then you need to book but if it's not then normally you can walk on. Get to the station a little early and try and get reservations for both, if you don't need them they won't give them to you.