brakes on 1996 Jaguar XJ6

was driving down road 45 miles per hr. when the brakes on all 4 wheels applyed themselves the pedel was fixed and could not apply at all. don't understand how this could happen all by itself did nothing was not even touching the brake pedel and was driving along in traffic, lucky to get to side of road safely and mad.

1 answer
I don't see any technical info from Jaguar about this, but my first thought is the master cylinder is applying the brakes. I've only seen this when people use the incorrect brake fluid, was brake fluid added to this vehicle recently?