Right, hopefully for the last time, here we go.
IET units don’t fit on the Pompey-Cardiff route. Quite apart from the fact that route clearance would be very difficult, given my experience of clearing Turbos on that route, the door cycle times would reduce the timetable to chaos. They really are best on IC workings, not on services with frequent stops.
There is no hope of getting extra units on the back of others orders either. Those options do not exist.
Until such time as any potential cl.175 deal is signed, there is no hope of getting extra stock onto GWR to replace the HST sets and boost formations on the services that need 90mph stock. The cl.158 units at TfW have been earmarked to go elsewhere and won’t be available in time anyway.
So what GWR are doing is stretching their available fleet to the limit and that is leading to short forms, both planned and unplanned. When replacement stock is made available to GWR (remember it is the DfT that make these decisions) they can dump the remaining HSTs, put the IET units back on existing IC services to boost formations and restore services such as Pompey-Cardiff to 4 and 5 coach trains with, probably, a mix of cl.158 and Turbo units.
So, if a Cotswold unit fails overnight in that future, chances are that a IET will replace it, not a Turbo.