The push rod has broken. Just get a new slave cylinder complete with push rod . It's the thing that operates the clutch from the slave cylinder.
Now you've posted a better picture, it's clear that the push rod has broken and pierced through the rubber boot. The new cylinder will include a new push rod.
When you fit the new cylinder, clean the hollow in the metal arm and smear some grease into it, and the ball on the end of the push rod.
I've not heard of the push rod breaking before. Has the clutch pedal become harder to push down recently?
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Ok so I have undone the bleed nipple pin (this is what was stopping anything from coming out of it ) and tried to pump the clutch to flush the system. The problem is when I lift the clutch back up it just seems to draw air back in to the bleed nipple.
The clutch is also still hitting the floor and not coming back up.