It's not so important to have 75mph units to replace 75mph on stoppers but to have units that can accelerate quickly on leaving stations.
Indeed, but we have plenty of everything.
Merseyrail 507/8 units free another 19 Class 313s from Southern, we have the vast majority of the Class 315 fleet being freed by crossrail, lots of Class 319/317/365 units being freed from FCC......
Even if every Class 313 on FCC is retained for the Moorgate service we still have more units than we will need.
EDIT:
Class 14x - 130 units - 75mph
Class 150 - 137 units - 75mph
Class 153 - 70 units - 75mph [Almost always attached to another unit]
Class 155 - 7 units - 75mph
Class 156 - 114 units - 75mph
Class 158 - 170 units. - 90mph
Class 159 - 30 units - 90mph
We have available:
Class 319 - 86 units - 100mph
Class 317/1 - 12 units - 100mph
Class 321 - 21 units - 100mph
Class 365 - 40 units - 100mph
Class 313 - 44 units - 75mph (from FCC assuming thameslink can cover Moorgate from its combined 377 strength)
Class 313 - 19 units - 75mph (from Southern)
Class 315 - 43 units - 75mph (ie the Shenfield metro fleet, assuming residual services will also be operated by Crossrail stock).
Which collapses down to 159 100mph units and 106 75mph units.
The 100mph unist should be able to cover the 90mph unit fleet between them, due to elimination of coupled working on many routes. (4x20 in place of 4x23 should not be catastrophic).
Leaving us with 106 75mph units to replace 358 75mph units (not counting the 153s).
Even though even the Class 313s are double the length of the Pacers that make up 30% of that diesel unit count, we are going to be short 75mph units and not 90/100mph units. Assuming ofcourse that the political will behind the electrification programme is not the bottleneck it is.
Although I doubt 319s appearing on SWT services in place of the Sprinters would go down very well.
Really we just need to order a lot of 3 car EMUs and accelerate the electrification programme drastically.
EDIT #2:
And we can free atleast one Class 158 by sending a Cl508 to the Lymington Branch line.
Should be better suited I think.
(And before anyone moans about repair work, they managed fine with the Heritage units didn't they?)