www.jec.org.uk

I have read the similar subject for Series 3.
Brakes stay on for about 1 second and seem to release if I blip the throttle.
I am leaning towards the air control valve faulty, or could it be the servo?
Any experience of this problem from other members?

I had the same problem. Cured by fitting a very light spring from Ken Jenkins in the servo bellows, thus helping it to release.

I don't know if this is where you read it but on page 24 of the April 2011 issue of the enthusiast magazine are Colin Ford's E-type Tips that he presented at the earlier seminar and one of which addresses sticking brakes on cars using the Lockheed servo. He advises a low cost & fairly simple job on the reaction valve piston which worked on my Series 3 that you might like to try first.