Bikes on trains in the UK

It would be good if everyone reported back on their train experiences too so we know whether the advice given on here is sound or as fantastical as the guards' often seems.

Brighton to East Croydon, Saturday afternoon, late Feb: Turned up on spec, no probs, no hassle, lots of room. Experiment hopefully to be repeated on a sunny Summer weekend in the not too distant future. Will report back! (Worst case scenario, I need to stock up on flapjacks and cycle home. Ugh.)