Brakes?

I have a B reg Ford Cargo 811 and the brakes (foot pedal) is not working no brakes , the hand brake works fine.

Bled the brakes getting fluid at all the wheels + air pressure is ok.

Still no brakes on the foot pedal, left it half hour then tried again, foot pedal worked ok and stopped the lorry, now the foot pedal is not working the brakes again, had to use hand brake to stop the lorry.

Need help please.