Truly a stab in the dark... class 25?
It's got to be something that's currently possible to see on the mainline and Mr Bridge is a stickler for the rules, so I don't reckon he'd try and pass a 25 off on us.
Could it be a 33?
Looks like a Mk.3 coach going by at speed.
Or a 220/221?
I'd say a class 220
Correct!