Rode to Aberystwyth and got the train home a few weeks back, checked on national rail enquiries site which will helpfully point you towards the operator – in our case it was Arriva Wales, it said capacity was two bikes and best to book so thought we better had. No-one asked a thing about reservations, and a couple of stops along the ticket lady asked us if we could squeeze our bikes over so they could get another one in. 🙂
Used to take a bike on the train between Birmingham and Banbury – as long as you use the right carriage no-one seemed to mind, only ever had one jobsworth on a Virgin train that had five or six bikes on give me any grief, and even he didn’t do anything other than grumble that he could make me get off at the next stop. Which, as that was the stop I needed, wouldn’t have been a problem anyhow. 🙂 Still, if it’s a route you’ve not been on before, makes sense to check their policy and reserve if that’s an option. 🙂