But if you buy new trains that are operationally comparable to the existing Azuma fleet, you don't actually have to use the new sets on the new service. They are just part of a bigger fleet.
One argument for going for 5-car new build might be it is easier to specify full compatibility with the Azuma fleet if you want to run 2 x 5-cars. Other potential bidders might say that you don't need that if you are running what amounts to a fixed 10-car set.
Given the comments about the over ordering if 5 coach units for GWR could the following be possible:
- offer to replace 2*5 coach GWR units with a single 9 coach unit (+4 middle coaches)
- use the spare 5 coach unit to create a new 10 coach unit (+5 middle coaches)
In doing so they could reduce GWR's lease costs whilst reducing the number of extra coaches they needed to build.
Obviously due to the IEP contact it could be tricky to do with that fleet, but it could be doable for the 802 fleet.
If there were 8*10 required, that would change the number of 5 coach units (802's at GWR) from 22 to 6 (or maybe 7 & still be down by 3 coaches in lease costs).
However if making changes to the IEP contact wasn't too hard you could create the following from the GWR 800's (36)
- 8*10 for LNER
- 12*9 for GWR (equivalent to 24*5)
- 16*5 for GWR
That would give GWR an increase in capacity to the equivalent of 40*5 coach units for the cost of 8 extra units.
Given each party is benefiting then there's likely to be an easier path than could of otherwise been the case.