If you take a look at the fast line trains from Euston in the two hours from 1700:
1700 to Manchester Piccadilly
1703 to Birmingham New Street
1707 to Liverpool Lime Street
1710 to Holyhead
1713 to Birmingham New Street via Northampton
1716 to Northampton (as far as Ledburn)
1720 to Manchester Piccadilly (overtakes the Northampton just before Bletchley)
1723 to Birmingham New Street (drops back a few minutes to stop at Watford Junction)
1730 to Glasgow Central
1733 to Liverpool Lime Street
1740 to Manchester Piccadilly
1743 to Glasgow Central via Birmingham New Street
1746 to Crewe
1749 to Birmingham New Street via Northampton (as far as Ledburn)
1757 to Lancaster
1800 to Manchester Piccadilly
1803 to Wolverhampton
1807 to Liverpool Lime Street
1810 to Holyhead
1813 to Birmingham New Street via Northampton
1816 to Birmingham New Street via Northampton (as far as Ledburn)
1820 to Manchester Piccadilly (overtakes the Birmingham just before Bletchley)
1823 to Shrewsbury (drops back a few minutes to stop at Watford Junction)
1830 to Glasgow Central
1833 to Liverpool Lime Street
1840 to Manchester Piccadilly
1843 to Crewe via Birmingham New Street
1849 to Crewe via Northampton
1852 to Birmingham New Street via Northampton (as far as Ledburn)
1857 to Manchester Piccadilly (ThFO)
(1900 to Manchester Piccadilly...)
Anyway as you can see it's a wonder that ever works at all.
Incidentally have those xx13 always been fast line all the way to MK? It seems that's done so two trains can run there instead of just one off-peak, with the xx20 overtaking the xx16 before it gets to Milton Keynes Central. It seems something similar happens at 1849, the 1852 goes fast instead of slow... but not to the 1752 because there is a 1746 and no 1846. Is there a reason why there is no 1846? There appears to be no room on the fast line whatsoever except the 7 minutes after the proposed xx33 and the 7 minutes between xx49 and the proposed xx57.
Could a fast line train go at xx54 and overtake the preceding train after Ledburn in the way that the xx20 does? Or is that only possible because the train behind the xx20 has the Watford Junction stop and thereby won't catch up to it so fast?
The 1713, 1716, 1746, 1749, 1813, 1816, 1849 and 1852 are timed for 110 (but some still on a 3 minute headway) what could be gained if they were 125? Probably not much... And also where is all of the freight in this?
I await the expert replies!
...and is why I believe it should only be built as far as Brum, as that is where it will make a real difference).
As I have pointed out before, this is a load of rubbish. What's your Glasgow Express going to do when it gets to Birmingham? It needs to link up with the main line somewhere north of Stafford - oh, what about Crewe...