Is number 4 St Erth? 

From an operational point of view, platform length and slow acceleration would be the main barriers I suspect.
8 Coaches is too long for a number of stations on the Portsmouth-Cardiff route for instance,  shame since a reintroduced Portsmouth to Penzance service on a HST^▸ (High Speed Train) would be quite a pleasant ride I'm sure.

As far as I'm aware the trips down to Fratton were at police insistence- Imagine the scene if the away supporters got to the station and saw that the 17.31 was a 3-car 158! 

Thanks very much. Been reading the forums for some time and so decided to join.

To be fair this is not the first time a FGW^▸ (First Great Western) HST^▸ (High Speed Train) has run over 3rd rail territory this year, dont forget they sent a HST set down to Fratton in January for the Portsmouth vs Swansea match.