Can you Fail your Driving Test on a manoeuvre?

Yes you can fail your driving test on a manoeuvre if you do something wrong, for example poor observations, speed, being in the wrong position or mounting the kerb. 
Manoeuvres are part of the driving test where you are the one that has complete control.  It is important that the car is kept as slow as possible so you can remain in control. All round observations are critical before and during the manoeuvre in case you need to stop for oncoming traffic or pedestrians. If you maintain a slow pace you can correct any mistakes you may make, if you are going too fast this may not be possible.