Both Stena Line and Irish Ferries have special tickets for train+ferry between Britain and Dublin, Ireland. Stena Line call it Rail Sail and Irish Ferries call it Sail Rail (I suppose that makes geographic sense). I have booked travel with a bike to Dublin through Rail Sail. I received my train tickets and confirmation the bike is booked for the ferry, but I did not receive bike reservations with my train tickets. For Sail Rail I will receive my tickets when checking in at the Dublin ferry port, and presumably they won't have a train bike reservation for me either. How do I obtain bike reservations for the railway part of the journey?
As I was travelling for work I've had to book through a travel agent, which insists that The train providers have advised me that they do not reserve a bike for travel but you can take this with you as luggage when travelling. That's incorrect at least for Virgin Trains and GWR, and perhaps others where bike reservations are mandatory.
My outward journey includes travel with South Western, CrossCountry, Virgin Trains West Coast, and Arriva Trains Wales. My return journey includes travel with Arriva Trains Wales, Virgin Trains West coast, and Great Western Railway. For those companies, I'm aware that bike reservations are mandatory or Virgin Trains West Coast and Great Western Railway, and recommended on CrossCountry and Arriva Trains Wales.