Recently picked up a 2007 Fiesta Zetec S when I bought the car it had an ABS light on the dash but didn’t effect the braking System (The light comes off and off whenever) 

However the other day I went for a drive and when I broke the brake pedal had gone stiff and my car was not stopping! I had to slam on the brakes and eventually it stopped (Luckily no one was in front of me) 

This has now happened on a few occasions but only when I first start driving, when it happens I turn the car off and pump the brake pedal and turn the car back on and everything is fine! It’s happened when the ABS light had been and off. 

Does anyone have a clue what could be causing this to happen. Every time I drive now I pump the brake pedal before setting about on my journey.

my thought is the brake need bleeding. But is there anything else it could be? 

if needs bleeding then pedal normally feels spongey and goes down further than it should. If with engine running the pedal feels hard and solid and does not go down as far as normal I would first suspect the servo is not working.

You do not say if petrol or diesel.  Diesel has an additional vaccuum pump on the engine to make the servo work. Petrol takes the vaccuum off the inlet.

However I am not saying it  could not be a ABS fault.