I never quite understood how Linslade was allowed 125mph EPS, when Kilsby wasn't, being limited to 110mph PS because of airflow issues.
The single bore DF at Linslade won't have opposing airflow, but the double track UF/DS will - although the DS is limited to 90mph.
Maybe it's tunnel length, or location of vents (if there are any) at Linslade, which allows a higher speed.
Linslade at 262m is not quite long enough to hold an 11-car 390 (266m), while Kilsby is of course much longer at 2209m and has 2 huge internal vent cavities.