Philh
In the Mk2 workshop manual this device is called a "differential valve assembly" and fitted with a "Pressure Warning Differential Switch".
In the Mk2 parts list up to 12/76 none was fitted then from 12/76 to 11/77 a 5 port assembly was fitted (Pt. No 73EB 2K493 CA) and from 11/77 a 4 port assembly (Pt. No 73EB 2K493 DA).
I believe the only purpose of the device is to light the brake fail lamp when either front or rear circuit fails.
I have not owned an Escort for some time but if I remember correctly on the later Mk2's the right front brake was fed directly from the master cylinder and the left front fed via the differential valve assembly.
I also remember asking at the parts counter about a repair kit and being told it is not a serviced part.
Interesting info thanks Phil.
I will be redoing the brake lines in the Denim pack soon, so the front left brake line doesn't run along the firewall where my turbo dump pipe would cook it. I'll probably route it beneath the radiator. Going by what you've said, I can delete this valve assembly without any concerns?