• I think first great western is the cheapest(32). Is the bike carrying free on trains?

    If your bikes are in bike bags for the flight I'd say keep them that way until you arrive in Bristol... They'll need to be in bike bags to travel on the tube/coach across London and then it'll save you having to worry about reserving bike spots on the train to/from Bristol

    (also leaves those reservations open to Londoners, not being selfish, just logical).

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