UK C180 (1999) Clutch wont engage

Symptoms: BAS ASR light on Clutch wont engage problem has deteriated with the biting point moving to the bottom of the pedal over the last year, now it is below (I presume)
Observations: brakes ok, oil level ok master and slave cylinder show no signs of leaks Tried: Bled the clutch, no difference.
Questions: How do I confirm that it is a hydraulic problem? If it is, how do I decide if it master or slave cylinder?

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