All this is very entertaining but clearly not the real reason.
The "Switch On GSM" sign at Oxford relates to the Go Slow Motor fitted to all trains operating Cotswold services. When trains promising 'High Speed' or even 'Turbo' operation were first introduced to the line, users were concerned that the essential nature of the Cotswold service could be compromised. As a result, a Go Slow Motor was fitted to ensure slower running. If, despite this, a train is making good progress, the GSM's emergency mode will kick in at certain predefined points (e.g. Evesham and Ascott) to delay the train by an arbitrary amount.
GSM is not fitted to all stock that can operate on the Cotswold line. For example, the Class 180 'Andante' trains are capable of delaying themselves by such expedients as catching fire, doors jamming open/shut, etc. etc. Consequently no assistance is required from the GSM.
I hope that's cleared it up.
I think that deserves some sort of prize for the funniest post in recent months..... top work Richard. I laughed so hard I very nearly followed through!!!!!!
