SW4730 : Penzance.
I don't remember seeing this type of train on the line but then perhaps I have a short memory. Apparently this train is a Metcam 102 unit and it made it's last journey from Plymouth in 1996. Where would I be without google :-)
More familiar to me is the 17:30 departure for London Paddington, Great Western HST which always seems to use this outdoor platform.