I recently spent some time in Teignmouth and had occasion to take a FGW train
to/from Exeter. I don't know what models FGW uses - the set going to Exeter was
definitely an older 2 car set, the return trip was still two car but much newer.

I thought most modern trains were diesel electric. That is, the diesel ran at
constant speed power an genset, which in turn provided electricity to drive
electric motors.

What seemed strange to me was that the engineer raised the RPM of the diesel
prior to leaving every station - almost as if he were engaging a clutch. Was the
the diesel directly driving the train?