Delivery of the GWR Devon and Cornwall bimodes in preference to the DfT ordered ones should help? As the Scottish sets will be short 4/5 car could some sets run with ex GWR mk3 and ex EC power cars till the ex GWR ones arrive or are there incompatibilities due to different modifications over time (door interlocking now)?
It's not a question of things being built in preference. Work on the two orders is going to be taking place in parallel much of time in 2017-18, at both Newton Aycliffe and in Japan.
All that needs to happen is that the gWr AT300 engines need to arrive early and have a longer lease period. They can then be fitted under the 801's (bearing in mind there will be 101 engines for the AT300's and a MAXIMUM requirement of 84 under the 801's assuming that all of the 801's become bi-modal), that then gives gWr until the summer of 2018 (rather than 2017).
IIRC the difference in the engines is down to the AT300's not being down rated whilst the rest are.
One year may not sound like much but it could be that gives NR enough time to wire up enough of the network to allow the introduction of enough EMU's to then start running the AT300's to Devon & Cornwall. Although it may then mean that the extra services to the West Country proposed still rely on a few HST's until getting on for 2020.
Given that gWr have 119 class 43's, they should still be able to use a few and still allow for 27 (54 class 43's) shortened sets to be used by Scotrail.
Given the latest report is saying that Cardiff-Swansea is all that will be missing after the end of CP5 and the initial IEP order assumed that it wasn't going to be wired up anyway I wouldn't have thought that it would be too much of a problem post 2020. Rather the problem would appear to be mostly a 2017-2018 problem.
This will mean that the new Northern franchise may have to use Pacers to closer to the 2020 deadline than they had originally planned.
Re the engines on 800s and AT300s, they are exactly the same unit, simply that on a Class 800, the normal maximum power output of each engine will be regulated down to 560kw (750hp), but if one of the three engines on a five-car set fails, then the other two automatically step up to the full 700kw (940hp) output to compensate.
On the AT300s, the full 700kw output will be available all the time - so it is perfectly possible to set up the 800s to run at a 700kw output all the time as well - though this would presumably mean a more costly maintenance and overhaul regime to allow for the extra wear and tear on the engines.
The full AT300 order is due to be delivered and in GWR service in time for the December timetable change in 2018 - which is well ahead of the bulk of the East Coast 800/801s, where delivery is not due to begin until September 2018 anyway, running through to 2020.
Whether the 801s are instead delivered to GWR as bi-modes looks like being down to what is said next month about the new schedule for electrification, notably where the wires will have got to by the time they are due to be delivered between March and July 2018. If the wires are closing in on Bristol by then, allowing a key destination to be reached under 25kv, the temptation may be to stick with an all-electric fleet, or at least only order a limited number of nine-car bi-modes.