Just thought I'd post experience of the actual trip here after my inquiry
last week. (First Great Western London -- St Ives via St Erth).
To summarize: everything went smoothly, but the value of reservations
remains dubious to me.
As someone had already written, the cycle spaces provided are nice and
sturdy. Sleeper has three, apparently for the total of the train, in a
little caged compartment that could easily fit twice as many bikes with a
different layout or without the holding racks. Sign explicitly says that
no more than three bicycles can be accommodated.
V friendly conductor asked whether we had a reservation for the bikes, to
which Nicola truthfully said she had been ascertained on the phone that
it wouldn't be a problem. We couldn't find anything about the bicycles on
any of the eight tickets that we got from the machine.
On the way back, daytime (not fast service) train had a compartment
holding 4 bicycles. We had actually cycled to Penzance and got on there.
Two other cyclists got on after us, so compartment was then full. No-one
asked about bicycle reservations.
Apparently, one is not allowed to lock the bike to the stand. We did so
and were called back via speaker system before the train took off to
open the locks. It was okay to lock the bikes to each other.
It was v nice to have the bicycles: most convenient trip I've ever had
within London before taking off to somewhere else. Of course, having no
stairs to navigate made it extra smooth at Paddington. We didn't cycle a
lot, but rode from St Erth to Penzance and then along the coast a bit on
the NCR 3. This was quite nice for leisurly riding, surface okay and I
recall not a single barrier. V nice view!
m.