UK Car Repair Questions? Ask a Mechanic for Answers ASAP
I would suspect that there is a fault either with the master cylinder or the ABS unit
1st try pulling the fuse for the ABS ( located in the underbonnet fusebox) to see if this makes any difference
if this doesn't there may be a bleed nipple on the ABS unit so open that to relieve any pressure, re-tighten and see if the brakes then operate and release
if they do then the issue is with the ABS unit
if this makes no difference then the master cylinder will have to come out for inspection / replacement
do you still need help?