Then it drove fine and it did it again a few days after. Straight away thought servo was on it way out. Drove ot for few more days and it seemed all okay So i did the servo test by pumping the pedal till it goes rock hard before i start the car, hold the pedal and start the car and the pedal should sink a little. Tried that, but, the pedal wouldnt go hard, but moves as should as soon as you start it. So again thinking is servo on it way out. Also when waiting at the light the pedal seem to travel down. There is a delay in braking. Took it to usual mechanic he said could be servo, could be caliper etc etc basically he had no idea 
and then took citroen/Peugeot specialist and they werent too sure, saying it could be the vaccum pump and that he has never had to replace a servo. He pulled the pipe off the vaccum pump and there was suction, there was also suction as the one way valve. He then showed me showed me the one off a picasso on the 2litre hdi engine but the vacuum pump on there had a lot more suction. So he said he would start at changing the vaccum pump first. So i sourced a 2nd hand one and changed it over in the freezing cold and it made no difference So i checked all the vaccum pipes and i have no vaccum going to turbo solenoid or egr solenoid, none going to the swirl diaphram either. I've read online of similair 406 owners who have had same issues and some have lost vacuum and replaced the servo and all is good again. I've inspected the front hoses and changed the disks and pads over as they needed doing and currently in process of changing rear shoes discs and pads. It brakes okay but there is a delay and the pedal sinks in traffic n pedal goes hard and then also if you press the pedal you can hear a slight hiss when engine is running. Any ideas?