XC loses money doesn’t it?
So blaming DfT is simplistic - you need a business case for increasing subsidy to pay for more trains.
Has the research been done to see who is travelling and how much they are paying? eg if it’s students and old folk on railcards or discretionary leisure travel then you are left with possibly reducing pollution/congestion. Could go BR and raise the fares to reduce overcrowding.....
If the problem is commuters then you need to look at possible suburban network Improvements and whether they would be better value.
Personally I think it will come down to green credentials and an empty factory leading to a political bi-mode order, or just hanging in for spare 22x - which still have a cost and need justifying.
As others have pointed out XC is making a profit, however even if it was making a loss the arrival of extra trains may not significantly increase costs but could generate enough extra income to pay for this extra costs.
As an example what's the cost difference between running a 4 coach 220 and a 5 coach 221?
Whilst there'll be extra fuel costs (as it's heavier, and not just because it's longer) and quite a bit higher track access charges the only "big" cost which does up is your leasing and servicing costs.
As your staff costs stay the same.
That means that each extra ticket sold doesn't have to cover much in extra costs but with space for over 50 more people seated per service there's plenty of scope to sell more tickets.
If XC were to get the 20 class 221's from Avanti (formally Virgin), that's likely to cost them somewhere in the region of £150 million a year in extra lease costs.
Personally I'd be tempted to investigate the cost savings from changing the 4 coach units to be all 5 coach units (i.e. reducing the number of end coaches which are being leased without increasing capacity by very much) following the introduction of the Avanti 221's.
That would mean a 5 coach fleet, making running the services easier as well as reducing the need for as much overnight storage.
In terms of net increase in the number of units or would mean that it dropped from 20 to 9, however every service would be 5 or 10 coaches long. Which for a lot of the services would be an instant increase in capacity.
Now whilst 9 extra units doesn't sound a lot it would mean that about 1/6 of all services could be (in addition to any editing pairings) run in pairs. If these were focused on the core it could be much higher than that.
Having not really increased my other costs other than fuel, leasing and servicing I probably wouldn't need to sell many extra tickets per train. However over some core route services I'll have added 300 seats, with 2/3 of the fleet having an extra 50 seats.